What to do with 250 seeds!

Question: I bought a packet of seeds that comes with 250 seeds! There's no way I have the space to plant 250 Silverbeet plants in my backyard, 10 plants maximum. What should I do with the 240 leftover?
Comment: Oh, and where are you?  You want to make sure you plant at the correct time of the year otherwise they might bolt on you.
Comment: What's the shelf life on the packet for the seeds?  Is there a seed swap place nearby?
Comment: @GrahamChiu don't worry it's the right climate, season, shelf life 2018
Comment: http://www.cbsnews.com/videos/saving-seeds-in-doomsday-vault/
Answer: Seed lasts quite a while.  It is said at least 30 percent of your seed is non viable the next year but I've seen maybe 10 percent or really normal germination.  Keep your excess seed in the dark, plenty of room between seeds, lots of air and between 40 and 55 degrees F.  If you know your seeds are dry you can vacuum pack them.
In two weeks plant another round.  Save the rest in their package.  No problem.  It is a good thing to have extra seed in storage.
Comment: Should I plant two in one spot or more or 1 in 1 spot?
Comment: Nope, planting 2 in the same spot means you will have to thin and that thinning can damage the roots of the one you want to grow.  I NEVER plant in rows!!  I like staggering across the tops of my 3' wide raised beds.  I even broadcast all my salad stuff to include beets.  I'd plant in staggered form like equilateral triangles and you'll get far more production than a row planting.  I even plant on the slopes of my raised beds.  Do plant closely such as one seed every 3" side and length.  You might have to thin but you'll have more success.
Answer: It depends on how much you like Silverbeet (Swiss Chard).  I never liked it much so I let ours go to seed, and it would keep popping up every year from self seeding.
If I wanted to grow some, I'd cast some over some seed raising mix ( sterile media ), and once the cotyledons have appeared, I'd prick out the healthiest to transplant into a 6 inch flat filled with soil compost mix planting in a dense hexagonal pattern.  Once they reach 6 inches in height, I'd then transplant the healthiest again to their final destination.  When they reach an edible height, I'd strip 20% of the outer leaves to eat leaving the younger leaves to keep growing rather then harvest the whole plant in one go.  If you really like the stuff, you could start the whole process again in a few weeks though 10 sounds plenty for a small family.  But it might be good insurance to do a second planting in case the first goes wrong with the main issue being that the seeds are planted at the wrong time of the year, and it bolts before you get much produce from it.
You can always keep some of the seed when yours will eventually bolt and use your own seed for planting in subsequent years unless it's a hybrid.
Answer: Do you have any seed swap events near you?  After making sure I retain enough seeds to get me through an emergency and another years sowing I package them up and take them to a seed swap event.
Answer: I generally stick leftover seeds in the refrigerator and that seems to work ok. Since Swiss chard is has a fairly low light requirement, so you could use the leftover seeds for microgreens in the winter

What to do with 250 seeds!


Lawn umbrella as a parachute?

Question: Just saw in a movie, a guy jumped off a building using a lawn umbrella as a parachute.  Would that work in reality?
Comment: For some values of "lawn umbrella" and "building" and "ground" sure. Certainly not for most of the lawn umbrellas I've seen, most of which are very weak. Some are actually designed to invert in heavy winds specifically to avoid damaging themselves. Further, you fail to specify "work" - is the intent merely to reduce the risk of death, or does it eliminate all chance of injury such that the person then could get up and walk away? Keep in mind that even a perfect lawn umbrella (weightless, doesn't collapse, etc) will still have a higher terminal velocity than a parachute.
Comment: Unscientific as it may be, I believe mythbusters did test this. Their result was the impact with the ground is fatal.
Answer: The science entertainment television show, MythBusters, investigated this claim in their 18th episode (in the 2004 season).
Wikipedia summarised their findings:

Opening an umbrella will slow a fall from a building enough to make it survivable: Busted
Though different umbrellas did slow a fall, the impact was still deadly. A real parachute was also tested but found to be unable to properly arrest a fall from only 60 feet (18 m). The best an umbrella can do is hold the person somewhat upright, causing less damage to the head.

The MythBusters team do an excellent job of promoting the concepts of testing claims through experiment, but they cannot be considered the most rigorous of scientific investigators. However, for a claim of this level of unimportance, it seems a sufficient level of evidence. If you were planning to risk your life jumping off buildings with just an umbrella, I would urge further experimentation!
Comment: I bet there are some MythBusters fans here with copies of the 2004 series. Would anyone care to expand on the summary, and describe what the experiment was and how it turned out? I have only vague recollections of the episode.
Comment: I recall they dropped dummies from various heights with and without umbrellas. Lower than 18m the umbrella had no measurable effect, from 18m and beyond it had an effect, but never enough to make a fatal fall survivable.

Lawn umbrella as a parachute?


Custom Profile Type and UPS Shipping Service

Question: I have an issue that I have been wrestling with for a few months now. I have a B2B site that needs a separate "Drop-shipping" shipping address field from the default shipping address that comes with commerce shipping. The fields need to be different because the client wants the default shipping address field to be constrained to only items in the users address book (controlled by the client, not the customer and created by the site admin when adding new registered users) but allow the second "Drop-shipping" added field to be an editable address form for drop-shipped addresses.
So, using the module "Customer Profile Type UI" I created the "Drop-shipping Information" profile type. Using "Checkout Pages" module I created a new page named "Drop-shipping Information" positioned before the checkout page, with a drop-shipping check-box. It is obviously the first page the customer will see when entering the check-out process, and before the checkout page, so that I can capture a Boolean value that will drive which check-out pane ("Drop-shipping Information" or just "Shipping Information" address fields) are shown on the checkout page.Then I use rules and "Change pane properties" to disable the "Shipping Information" pane if the user has selected "Drop-shipping" on the first page, and vice-verse if not. All of that works properly.
The problem is, when "drop-shipping is selected and a valid address provided, when moving from the checkout page to the shipping services page (with UPS enabled and tested to return rates), it returns the rates for the "Shipping Information" address, and not the "Drop-shipping Information" address.
I realize that rules may only be hiding the default "Shipping Information address form (which is including a default shipping address from the customers account profile) ... but how do it make it use the address in the "Drop-shipping Information" address form instead?
Not sure what I am doing wrong, and I see no configuration options to change the behavior. Can someone tell me what I might be missing or perhaps provide an alternate method (that doesn't require custom coding) after reading the details of my requirements above? Either way, you should know that I am not a developer, and could use at least some mid-level instruction on what I have missed or need to do.
Thanks in advance for any serious help. :)
Answer: Commerce UPS calls commerce_physical_order_shipping_field_name($order) to determine what field holds the shipping profile for a given order. That means you can then use Commerce Physical's hook_commerce_physical_order_shipping_field_name_alter() to specify a per-order shipping profile field.


Is the small alphabetical index on mobile phone lists usable

Question: I'm working on several mobile filters with long lists and wondering if this pattern that's been used in most mobile phone contact lists is actually usable? It seems too small to get an accurate press on any letter in the list. What's your take on this? If normally users are using this for their usual mobile tasks on the native OS then it should be a good pattern to adapt, right?
Comment: Good question! I'm interested to see what responses you get. I asked my Dev colleagues to remove this index from one app that had long lists, because it didn't work very well for a handful of people I observed (in a statistically invalid sample!), and because my lists had a Search box. The iOS human-interface guidelines say the index is optional. See **Table View** on this page: https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/ContentViews.html#//apple_ref/doc/uid/TP40006556-CH13-SW1
Comment: I never had a problem with it because you can hold down your finger and scroll to what you actually wanted. Also on android you can hold down and swipe to the left you change the second or third letter. You can hold down, scroll to M, then move a bit to the left and change the second letter and thus accessing the Part where the Entries begin with MI and if you really have an enourmouse collection you can do this more often until you got "MICE" or whatever you were searching for. Bit at this point you propably would've used the search function long time ago
Comment: Jonas yes you probably didn't have any problem using it. Most of us here are power users but I'm curious if this is intuitive to the average user
Answer: Personally I use this all the time. While it would seem too difficult to have accuracy these are actually treated like a smart scrollbar that scrolls not by pixels but by letters. Users are able to drag down on the letters to pinpoint the letter that they would like.
If you have the resources to build this in your project I would say that it would be highly beneficial.
Like Jonas Dralle said this feature is not just available on ios but also on android (other systems too). Depending on how big your lists are it may be better to add advanced search rather than this (or maybe in addition to this). It all depends on what kind of data you are handling, the larger and more complex the data the better it would be to use search. If the data is too small users might feel overwhelmed by the extra ui elements.
Answer: I've used both Android and iOS, out of those two I find the Android alphabet scroller easier to use.
It's all because as soon as you press the scroll bar, the letter that's selected appears on the center of the screen. (Position might change based on the device)

This tells me,

I have selected the contact scroller and nothing else.
I can drag the scroller and the letter on the center tells me exactly where I'am.

This feature solves your problem of the letters being too small to get an accurate press.
As for whether users would understand an alphabet scroller or not -

Younger audiences are getting better at navigating applications and
finding how things work. Having spent longer hours on smart devices browsing different applications, they would possess the experience needed to
identify how this would work.
As for other users, any user who knows or has used a contact book
or something similar are likely to know what it is and what it does.


Who posts in the "Backup Room -The H-Bar"?

Question: While visiting the chat section I found a room named Backup Room – The h Bar.Though it seems to me that people don't chat over there rather I found that list of hot network questions are posted. But who post these? Is it automatic? Why is it greyish rather that blue in color?
Answer: That room is the chat room associated with Physics Meta, in the same way that the HBar is the chat room associated with Physics.  That's probably why the color scheme is different.
There was a period where the HBar was one of the most active chat rooms on the SE network, and it wasn't uncommon for two independent conversations to develop at the same time with enough activity that it was confusing about who as talking to whom. During those times the participants in one conversation might decide to move their topic to the "backup room" to make things easier to follow. That was most common during our weekly scheduled chat sessions, but it happened other times, too.
Around the time that I was elected moderator, the HBar needed a lot of moderator attention, and we started using HBar and the "backup room" in a way similar to the divide between Physics and Physics Meta. In HBar people talked about physics, and cooking, and politics, and life; if someone's feelings were hurt and there needed to be a conversation about what kinds of things were or weren't okay to say in chat, whether it had been appropriate to flag or delete a message from someone, and so on, we would have that meta-conversation in the meta/backup room so that main chat could get back to physics and cooking and life.
As our community's understanding of itself matured, we needed the backup room less and less often. Sometimes a user would post an HBar-like question in the backup room and no one else would reply for a week or more. When a user wrote a bot to identify new Hot Network Questions (only a few months before changes to the SE API made that information available in a more robust way), we decided to allow the bot to post in the backup room because it existed but didn't get much traffic. Since the HNQ bot now posts in there a few times a day, I no longer know whether new users still try and fail to chat there. We haven't needed it for meta/moderation purposes for quite a while, for which I'm glad.
I suppose the current state of things is pretty confusing-looking for a new user who doesn't have that history. If anyone has a suggestion about a change to make so that the Physics Chat ecosystem makes more sense to new users, they ought to propose their change in a new Meta question and link it from this one.  But I'm happy if it's just a curiosity.
Comment: I was just exploring the features of the site and gathering information about it from old meta posts but didn't found any (about this and some other topics) so just asked on the meta. Though I still have one question : What if I need to ask you about something in future-1)Should I make a meta post? 2)Ping you in the H-Bar? 3) or in the back up room? (Nothing sort of serious just some curiosity about the site!)
Comment: While searching searching about the backup room in the h bar I found something called AMA and currently think that these chat session involve famous physicists (like Heather, Mithrandir, etc.) (though I don't know anything about them (Sorry!)) and I want to ask whether these AMAs still occur? and if so then whose next?
Comment: For questions about site mechanics and site history, this Meta site is the right venue. Brief questions might get answered in the HBar (immediately if it happens to be busy, or after a delay if no one is around). The "ask me anything" sessions were organized by a site user, and were more about getting to know our own community members than about recruiting outside famous people to chat.


When arriving to the Schengen area I told the immigration officer I'm staying for a month. Would it be an issue if I stayed for a longer time?

Question: I have 90/360 multi visa in the Netherlands. I arrived to learn English in a month course, but course was postponed for a week. I told to immigration officer in the airport that I would stay for a month. Now I see that I need to stay here for one more week because of postponement of the training. Do I have to tell the immigration office about the situation? Do I have to register at the nearest police station office?
Comment: Today I went to Vreemdelingenpolitie (Johan Huizingalaan 757 Amsterdam 1066 VH). They work from 8 to 11 a.m., and it is important, because it's very hard to find them (I was late yesterday), so I advise you to go there in advance.
They told me that I can be in Amsterdam for 90(!) days and put a stamp in my passport.
Answer: As long as your visa is still valid you are allowed to be in the Netherlands. So shouldn't get in to trouble over an extra week, just don't exceed those 90 days.
Also, your answer to the airport official probably isn't even registered anywhere. They ask random these kind of questions to make an assessment of the person in front of them, not because they want to know the answer...
But if you stay once your visa expired you will likely get problems, especially when they check your papers when you are going back home.
Answer: As Avee said, the questioning by immigrations isn't generally recorded unless something suspicious is found and it gets extended into a police investigation (at which point you'd have been taken apart into an interrogation room at the very least).
When in doubt about your visa status, do visit a police station and ask. They can help you either clear things up or direct you to someone who can.
Your visa is good for 90 days ("multi" I guess means multiple entry visa?), so you're good as long as you don't stay more than 90 days in the country (or indeed the Schengen area). You've been 30 days, need to stay another 7, that's less than 90, so unless you have in the past spent more than 53 days already since the visa became active, or unless the 7 days would mean you're overstaying the last date the visa is valid, there should be no problem.
Comment: Police? I thought that would be [IND](http://www.ind.nl/en/Pages/Default.aspx)
Comment: IND yes, police might be easier to get to though, as IND has far less offices and they're not clearly marked (might even be there's only the headquarters in the Hague/Rijswijk which is part of the ministry of Justice building, I am Dutch and have never seen any office of them marked anywhere in the country). They also have a page about short term registration (not visa application, but arrival registration) procedures on their website (Dutch only) https://www.politie.nl/melden/kort-verblijf-vreemdelingen.html
Comment: They have offices but I believe fewer than some years ago (the one I once went to in the Hague does not exist anymore): http://www.ind.nl/contact/adressen/Pages/default.aspx I suppose contacting the police cannot hurt, I have always found them particularly helpful compared to other police forces I know elsewhere in the world.


Kinetic energy Hamiltonian in second-quantized form and the Dirac delta function

Question: I'm trying to transform the kinetic energy Hamiltonian to momentum basis. Starting with:
$$\hat{T} = -\frac{\hbar^2}{2m}\int d^3r\ \hat{\Psi}^{\dagger}(\vec{r}) \nabla^2 \hat{\Psi}(\vec{r})$$
I can expand the field operators in terms of momentum eigenstates, since the system is translationally invariant:
$$\hat{\Psi}(\vec{r}) = \frac{1}{\sqrt{V}}\sum\limits_{\vec{k}}e^{i\vec{k}\cdot\vec{r}}\hat{a}_{\vec{k}}.$$
I get:
\begin{align}
\hat{T} = &-\frac{\hbar^2}{2m}\frac{1}{V}\sum\limits_{\vec{k}_1,\vec{k}_2}\hat{a}_{\vec{k}_1}^{\dagger}\hat{a}_{\vec{k}_2}\int d^3r\ e^{-i{\vec{k}_1}\cdot\vec{r}} \nabla^2 e^{i\vec{k_2}\cdot\vec{r}}
\\= &\frac{\hbar^2}{2m}\frac{1}{V}\sum\limits_{\vec{k}_1,\vec{k}_2}\hat{a}_{\vec{k}_1}^{\dagger}\hat{a}_{\vec{k}_2}\vec{k}_2^2\int d^3r\ e^{-i({\vec{k}_1}-\vec{k}_2)\cdot\vec{r}}
\\= &\frac{\hbar^2}{2m}\frac{1}{V}\sum\limits_{\vec{k}_1,\vec{k}_2}\hat{a}_{\vec{k}_1}^{\dagger}\hat{a}_{\vec{k}_2}\vec{k}_2^2 V\delta(\vec{k}_1 - \vec{k}_2).
\end{align}
Here I don't see how this expression should simplify to
$$\sum\limits_{\vec{k}}\frac{\hbar^2\vec{k}^2 }{2m}\hat{a}_{\vec{k}}^{\dagger}\hat{a}_{\vec{k}}\, ,$$
given that the sum over $\vec{k}_1=\vec{k}_2$ gives $\delta (0)=+\infty$. Did I make a mistake somewhere? Could this be due to the delta function switching interpretation between a Dirac and a Kronecker delta?
Answer: Unless you are, for some unknown reason, insisting that your momentum spectra are discrete, those sums of $k_1$ and $k_2$ should really be integrations. This that the immediate consequence of resolving the difficulty with the Dirac delta that you are describing.
I will also note that $\Psi$ is generically a function of both space and time, even in the canonical formalism. So you should really be expanding by Fourier modes in time as well. All of this would be worked out in detail towards the beginning of most standard references on quantum field theory, such as Peskin and Schroeder.


Dying leaky ReLU

Question: I am trying to train a deep neural network but I am having dying ReLU problem. I am using leaky Relu but still have the same problem. Isn't leaky relu supposed to not have such problems?
Answer: Actually, it is not possible that leaky ReLU suffers from a dying problem unless the slope of the negative inputs is so small. Try to use something like 0.2 for the slope of the negative part.
On the other hand, I believe your problem is not dying ReLU, because if it happens, almost all of your activations will output zero. My answer is basically telling you that your outputs may be so small and they change so slowly.

Dying leaky ReLU


Does anyone know of any kernel/driver programming tutorials?

Question: I'm interested in using the RPi to teach myself hardware level programming. I've searched the internet for some tutorials for RPi but all I find are general "how to compile the kernel" tutorials. I'm more interested in actual "how to write kernel code/device drivers"-type tutorials. Are there specific tutorials for RPi, or would any *nix tutorial for hardware level programming suffice?
Comment: @Jivings: The suggested duplicate doesn't address either part of my question. Elinux and CAS doesn't seem to have anything about RPi kernel programming while GPIO programming barely scratches the surface of writing drivers. Additionally, there is no mention in the suggested duplicate of RPi vs. general *nix tutorials.
Comment: Posible duplicate of [Is there a collection of teaching materials?](http://raspberrypi.stackexchange.com/q/200/40)
Answer: I don't think you'll find a better resource than this unless you know somebody personally.
Enjoy
P.S. In case the link dies, the book is called Linux Device Drivers.
Comment: This does look very good, I've always been a fan of the O'Reilly series.
Comment: So I take it that driver programming in the Linux kernel will transfer pretty easily to Raspbian?
Comment: Raspbian is basically just a smaller Debian distribution compiled with special parameters specific to the hardware on the Raspberry Pi. So yes it should, though I am not an expert on either driver programming nor the Raspberry Pi so let's wait for someone more knowledgeable to chime in.
Comment: Seems very outdated (Kernel 2.6 and from 2009). Anything more up-to-date?
Answer: I have just found something from the University of Cambridge.
It's easy to follow and very well made introduction how to put your first OS together: http://www.cl.cam.ac.uk/freshers/raspberrypi/tutorials/os/
Comment: WOW! :) This is brilliant!
Answer: In addition to the LDD book, you may also look at the training course documents at free-electrons.com. There all the course materials are open sourced. Quite suitable for who has started a little bit into linux kernel programming, or who is looking for deeper and wider understanding of specific topics/areas.
To start with, you may look at least the first two courses:

Embedded Linux System Development course.
Linux Kernel and Driver Development course.

And don't forget the lxr source code cross-reference site on free-electrons.com, where you can check source code for various kernel versions.
If you favor an IDE especially NetBeans or Eclipse, and know how to run perl scripts and Makefile, you may look at my project Nbk tools on github.com. The script enables you to fully index a kernel project with NetBeans C++ kit. It greatly helps improve the experience to understand more of the source code internal structures and relations. I usually make a minimal configuration of the kernel plus the specific device I'm looking at, and make a build and do an index in NetBeans just for analyzing the kernel code. While do the actual development in another project. This script is tested directly in NetBeans, but with Eclipse the idea would be the same (you need to modify the script to suit Eclipse).


Meeting place in CDG

Question: I will be arriving into terminal 1 at CDG and other family members will be arriving into terminal 2B.  Where is the best place to meet to after collecting our bags and to meet our shuttle to the city?
Comment: I would meet closest to the terminal where the group arriving last lands, so those arriving first have the time to get to the other terminal. Other than that, I can't see any reason to prefer one over the other.
Answer: Roissy-Charles de Gaulle (CDG) is not the easiest in which to do this but there are many official, signed meeting points in each terminal. They're landside, after baggage claim and close to the Aéroports de Paris information counters.
You might arrange to meet at the shuttle; you don't say which one you're taking, or who is arriving first/earlier.  Terminal 2 is very large, and you get to it from Terminals 1 and 3 by taking the CDGVAL airport shuttle trains.
Referencing the airport map, you can select a meeting point that works best for you and your family, depending on arrival times and gates, and your shuttle connection. They are located in:

Terminal 1 Arrivals level, close to Exit 34
Terminal 2A Opposite Exit 4-5
Terminal 2C Opposite Exit 5-6
Terminal 2D Opposite Exit 6, opposite Exit 7 (two baggage claim facilities)
Terminal 2E Arrivals level, opposite Exit 8-10
Terminal 2F Arrivals level, opposite Exit 8-10
Terminal 2G Main hall
Terminal 3 Arrivals hall

Meeting place in CDG


Need help interpreting my soil test results and fertilizer recommendations

Question: The guy from the lab told me to use 13-13-13 fertilizer. my Lawn is 4000 sq feet, 1 (8 pounds/1000 sq ft) in April and 1 in May end. And then 1 each in September and October end. Also, use liquid ironite.
Other stores have different recommendations like adding Pete Moss or gypsum.
Comment: How much is "1"? Unless we know that, the advice could be anywhere between "irrelevant" (too small to have any effect) and "fatal to most plants".
Comment: What are you cultivating? This is more important than soil analysis: every plant has own needs, and so you should give them what they need. Then balancing soil will help (as "reserve", but also because plant cannot absorb all nutrients [you need some basis]).
Comment: @alephzero - I have updated my results with Nitrogen levels and 1 means 8 pounds/ 1000 sq ft, my lawn is 4000 sq ft.
Answer: Depends on what you want to grow and how fast you want it to grow. The most noticeable item is the alkaline pH of 7.8 : most plants are best near neutral ( pH 7) or slightly acidic. That is why gypsum and peat moss were recommended ; both tend to make soil less alkaline / more acid ; good recommendations. If you are growing grass you need some nitrogen ; I would first put on 13 13 13 or 10 10 10 (very general standard products) then later put on lawn fertilizer ; high nitrogen something like 20 5 5 . The numbers are not that important as long as the first one ( nitrogen) is largest. Pretty good test results , about the only low items are N, P, K ; the elements that are most absorbed by plants and most easily replaced with standard fertilizers.
Comment: I was reading this article on Iowa state university - hortnews.extension.iastate.edu/2016/02-12/soilpH.htm it says - Elemental sulfur is the safest option to decrease soil pH. and I found some products for that, but the Lab specialist said, your pH will go back to where it is in a year, So he stressed on using liquid Ironite. Will using the Elemental Supphar not reduce my pH? or have no effect on my soil??
Comment: Gypsum / calcium sulfate will slowly dissolve for a few years . Also, organic mulch like peat will continue to release organics acids for some time. But. it is difficult to change the pH of a soil permanently . So, it is a continuing project to have a very nice lawn  ( my lawn is pretty bad , so I mostly have azaleas and other shrubs.)
Comment: I don't mean to be critical, and I'm not vying for the chosen answer here, but gypsum has a neutral pH (not an acidic one), and while it might actually reduce the pH of an alkaline soil a little, there are other ways to acidify soil (without adding calcium), such as elemental sulfur.
Answer: Well, you certainly don't need gypsum. Gypsum is calcium sulfate, and your calcium is already very, very high.
Your phosphorus is low.
Your sulfur looks very low, though. Adding some sulfur would help to acidify the soil further (your pH is a bit high). Sulfur is usually what people use to acidify soil. It takes a while for it to work, though. Plants also use (and need) sulfur.
You could probably use more copper (don't overdo it, as it can hurt your plants and stop roots from growing; you don't need much). Low copper could make plants more susceptible to disease, and the fruits might not absorb as much water. It can also affect taste.
Peat moss is great to add organic matter, and it is acidic, but I can't say what long-term effect it has on soil pH; for the short-term it seems to help, though.
Your potassium, magnesium, boron, zinc, sodium, and iron look fine.
Your manganese looks much higher than necessary, but that's probably not a big deal when you have alkaline soil (manganese becomes more available the more acidic the soil gets). So, if you acidify too much, it might be a problem and cause toxicity symptoms.
I don't see any mention of your nitrogen levels. With high calcium, you probably want a good supply of nitrogen, phosphorus, and potassium. Adding some extra potassium isn't going to hurt even though your potassium levels are fine already (unless you add way too much). Extra organic matter should also be beneficial.
Note: I'm not an expert on ppm levels, but I googled what the ideal levels are supposed to be and compared those with yours. The ideal ppm levels aren't exactly the same for every soil type, but I'm guessing my analysis is correct. Some nutrients need to be in balance, too (such as manganese and iron).
I have no idea why they recommended iron, but I think adding iron is a bad idea here. As for the gypsum (calcium sulfate), the sulfate in the gypsum would be good, and it might be good for your soil texture, but it would add extra calcium to an already too-high supply (granted, gypsum has a neutral pH; so, it wouldn't raise your pH).
If you have availability problems with a particular nutrient, due to the alkaline soil or something, you can try to do foliar sprays of fertilizer to get around that (make sure the fertilizer can be used as one, and that you use the right ratio of fertilizer to water).
Comment: "LIquid ironite" is basically a high-nitrogen fertilizer (NPK 7-0-1) plus a bit of iron. One recommended use is getting an "instant" green lawn from the high N content. But the soil analysis doesn't include any results for N and presumably the OP isn't growing a lawn (otherwise the 13-13-13 recommendation makes no sense) so why ironite was recommended is just a guess. Maybe it's a high-profit-margin sales item...
Answer: The main problem is there is no value for nitrogen... so without nitrogen, it's difficult to reconmand a fertilizer to fix your soil.
so far we know that your dirt is low on phosphorous and potassium..... that is probably why store recomand 13-13-13 fertilizer, it's a safe bet that would fix the low phosphorous and potassium but it might lead to adding too much nitrogen which might cause problem if you are potting the plant..
but if you are growing directly on the ground, than no need to worry about nitrogen build up, the earth will just absorb the excess...
Comment: I have updated my question with the Nitrogen results now.
Comment: 7.9 parts per million of nitrogen is very low, I understand why 13-13-13 and Liquid ironite is recommended.. you can follow the shop recommendation, alternately you can look for a fertilizer that could provide more nitrogen, something like 16-13-13 or 8-5-5... that way you don't need to fertilize twice.
Comment: I was reading this article on Iowa state university -
https://hortnews.extension.iastate.edu/2016/02-12/soilpH.htm
it says - Elemental sulfur is the safest option to decrease soil pH. and I found some products for that, but the Lab specialist said, your pH will go back to where it is in a year, So he stressed on using liquid Ironite.Will using the Elemental Supphar not reduce my pH? or have no effect on my soil??
Comment: I dont think you need to worry about the PH of your soil, it's pretty much ideal for most plant. Liquid Ironite doesnt change PH of your soil, it's a 7-0-1 fertilizer with added iron.. so it's basically ideal for your soil when using together with a 13-13-13 fertilizer.


Building a Circuit that takes constant mA

Question: I want to discharge a battery at a constant C rate (0.2C) the battery is 3.7V and 380mAh. I did some calculations and found out that the current the circuit will need to take is 76mA. I am planning to build this with LED's. I am not sure but from what i know LED's take a constant current, i am not sure if this is 20ma or 15ma or something else. Also I am not sure if I should connect them in series or in parallel. Can someone help me come up with a circuit I could make that takes up a constant current of 76mA.
Any suggestions of LED's i could buy off amazon do to this would also be helpfull
Comment: You are confusing two things. LEDs and diodes aren't constant current. They are constant voltage which means you can drive them with constant current supplies to ensure they do not burn out, because their voltage drop is constant and will make no attempts to change to limit current through them.
Comment: This is an X-Y problem. It would be better to ask for advise about the original problem rather than asking how to implement a solution that may not solve your problem.
Comment: LEDs should be operated by constant current, they do not provide a constant current characteristic by themselves
Comment: Ah, what you need is a CCS - Constant Current Source. For LED newbies, I would recommend to start off reading http://lednique.com.  Happy learning. Cheers.
Comment: A Lithium battery cell is 3.2V when almost completely discharged and is 4.2V when fully charged. 3.7V is half a full charge. Why so do want to discharge it more? If its voltage becomes less than about 3.0V then it is ruined and might explode or catch on fire if charging is attempted. Read about it at www.batteryuniversity.com .
Answer: The most you should discharge a Li-ion cell to is about 2.8 to 3.0V to prevent damage to the cell.
Here is a very simple circuit that maintains a fairly constant discharge rate from 2.8 to 4.2V (and beyond).

simulate this circuit – Schematic created using CircuitLab
R2 biases D1 (actually an IC shunt reference that regulates at 1.24V) and provides a small amount of base current for Q1. Q1 provides the remainder of the base current Q2 requires.
R1 is chosen so that 1.24V/R1 ~= 76mA. A bit of current that is not metered goes through R2 so the current is not precisely constant.
Here is a quick LTspice simulation:

The circuit will typically work well below 2.8V-3.0V so you need to provide some means of cutting off the current before the cell is damaged.

Just for comparison, as I already had it set up, here is @Michal's circuit simulated:

It's possible that he got different results depending on the models used.

In real life, it would be much nicer to make a circuit that operates from an independent regulated power supply such as 5.0V which would eliminate both the low voltage limit and most of the slope in the current-voltage line. It would also be easy to incorporate a low voltage cutoff.
Answer: You must drain it to resistor because the Leds rapidly decrease conducting under 2,8V. I expect you want to go lower. Probably simplest constant current circuit:

R1 and R3 about 2Wats power rating


How do I make infinite lava?

Question: I want to make an infinite lava source,like with the water. If one puts 2 blocks of water,they will fill another block completely. Lava does not do exactly the same. If this is not possible,lava is limited,not like water. Is there a way to do this?
Answer:
If this is not possible,lava is limited, not like water.

This is correct. You cannot generate lava in vanilla minecraft without using commands, or creative mode.
However, although lava is limited, it is found in massive quantities in the Nether. So it is theoretically possible to transfer all the lava you want to your world, albeit long and boring.
Answer: You can't lava is not an infinite resource (barring going through infinite chunks).
Source: https://minecraft.wiki/w/Lava

How do I make infinite lava?


Reason behind Chrome not running in root user in kali Linux?

Question: Why does Google Chrome not run as root user by default in Kali Linux? Is it a security issue?
Comment: Quick question for you - do you think it should run as root? What implications would that have?
Comment: Safesploit - what do you mean? I certainly didn't try to answer the question. I commented, specifically asking them to consider something.
Comment: @reed No. The problem is that Kali is not designed to be secure, and so runs _everything_ as root by default whenever it can. People who use Kali in this way are just asking to get pwnt.
Comment: @safesploit my assumption is the down views are because least privilege is a very well understood basic premise of security and the OP maybe hadn't done sufficient research.
Comment: @RoryAlsop I do not see how this answered their question. Given they are a new user, they may also be new to the dangers of root. Particularly running graphical applications as root, and the dangers of privilege escalation.
Comment: @RoryAlsop I just feel the number of downvotes towards this question to be unreasonable, as it asks a valid question. Which despite research looking for a duplicate question, the general theme I came across doing this was 'don't run web browsers as root' without giving clear reasons. I am curious myself to why the developers put these safeguards in place, to begin with, while others have not. Particularly when I found quite simple bypasses.
Comment: I wonder why somebody would ever need to run a browser as root. Are there any cases when this would make sense?
Answer: It's basically because of the principle of least privilege (see for example: https://en.wikipedia.org/wiki/Principle_of_least_privilege). There is no reason to give Chrome all the power and capabilities that root has. More privileges mean more trouble in case something goes wrong.
As a side note I have to say though, that I am skeptical about the advantages of low privileges in the specific case a typical Linux desktop gets compromised, because the typical desktop user regularly uses sudo to basically get all the privileges. The user just trusts sudo, but sudo is just meant to be used for convenience, not for real security, because it doesn't provide enough separation of privileges. But this is a side note, regarding a specific issue. In general the principle of least privilege always applies.
Comment: Even with bad use of `sudo`, low privileges can still be beneficial. For example, imagine a malicious process is executed while the user is doing something sensitive (transferring all their Bitcoins or whatever), and only later do they use `sudo` in a way that lets the process get root. By the time it gets root, it may be too late.


Could you charge a recharable battery with a voltaic cell?

Question: In class we were learning about voltaic cells and my chemistry teacher joked that after modern society falls, we'll be the only ones who can recharge batteries with simple voltaic cells. And this got me thinking, is this possible? Could I create a salt bridge cell, attach wires to a store bought rechargeable battery, and charge it? I'm really curious and I can't ask my chem teacher as he's in the hospital recovering from an emergency appendix removal
Answer: Any source of electricity of the required voltage and current could be used to charge a rechargeable ("secondary") cell. A home-made "primary" cell would work (though you might need a few in series to provide the needed voltage).
For that matter, you can generate DC to charge the cell many other ways:

Using a thermopile, e.g. from copper and iron wire
Magnetohydrodynamically, e.g. with flowing salt water and a magnet
Using a photovoltaic panel...


The effect of coupon frequency on the price of a bond

Question: I'm trying to prove how coupon frequency affects a bond price.
I get it intuitively but I have not found a math proof.
Could you help me?
Comment: Small hint: How does a cash flow series $\sum_i c \times e^{-r*t_i}\Delta(t_i)$ converge to an integral? And then solve that integral.
Comment: As an investor, rather than receive $C$ once a year, you would prefer to receive $C/2$ twice a year, or even better receive $C/n$, $n$ times a year. You can re-invest or consume the coupon sooner, a good thing in a world of positive interest rate. So the bond price goes up with $n$. But the effect is small, and becomes ever smaller as $n$ increases. (Think of your salary: how much would you benefit if it was paid weekly rather than monthly: not very much).
Comment: @noob2 I would argue that the *preference* effect should already be found in the time value of money. A bond is a scaled sum of discount factors. As these are non-increasing with time to maturity, you get higher PV with higher frequency (as you suggest). I am wondering whether that's simply the mean value theorem at work...
Answer: Let us assume a plain vanilla bond with maturity $T$ and fixed coupon rate $c$ and a unit notional of $1$. The bond pays the coupon at a some frequency $f$ which translates to payments every $\Delta(t_i)=t_i-t_{i-1}=1/f$ years. Further, assume a fixed continuously compounded interest rate $y(t)$ with corresponding discount factor $D(t)=e^{-y(t)t}$.
Then the bond price can be written as:
$$
PV=c\sum_{i=1}^N D(t_i)\Delta(t_i)+D(t_N)
$$
Assuming a monotonic discount factor function, i.e.
$$
e^{-y(t)t}\leq e^{-y(t')t'} \quad \forall t>t'
$$
the present value of the bond is strictly increasing in the coupon frequency as we are sampling more and more from the higher discount factor values.
As we increase the coupon payment frequency to infinity, $f\to\infty$, the time step becomes infinitesimal, $\Delta(t) \to dt$ and the present value function converges to
$$
PV=c\int_0^Te^{-y(t)t}dt+D(t_N)
$$
Here, the present value of the bond is maximized.
Comment: Great! But what if the discount factors _D_ were sometimes allowed to increase with time (negative interest rates)?
Comment: Hi @DimitriVulis Yes, that would make this discussion more complicated. But since this seems to be a finger exercise in the first place, I would like to **assume** that discount factors are non-increasing ;-)
Comment: exactly :) :) :)
Answer: The frequency is static indicative data. It does not normally change during the life of a bond.
If the frequency changed in a debt restructuring, then it would be highly unlikely that the frequency would be the most material change or that we could isolate its effect,
I recall Indonesian (USD-denominated) floaters where the issuer had the choice at the beginning of each coupon period: either pay 3M USD LIBOR + spread in 3 months, or pay 6M USD LIBOR + spread in 6 months. But this option was known and priced in at issuance.
If you meant to ask: if two bonds have "the same" indicative data, except for the frquency, and trade at "the same" yield, then how does the frequency difference afftect the yield-to-price, then both "the same's" are imprecise:
If you're comparing yields of two bonds having difference frequencies, then you may choose to convert one yield to the other bond's frequency. Or not. Not in the U.S., but in most other bond markets, if you're comparing yields of quarterly, semi-annual, and annual bonds, you first convert them to the same frequency. Yields are are "the same" before conversion are not "the same" after conversion. You may want to work out the price difference if the yields are "the same" after conversion.
If you're quoting "6% a year coupon paid semi-annual" then in most markets the convention is "6/2=3%" coupons, but, for example, in Brazil it means "(1+6%)^(1/2)-1=2.95%" coupons (see, for example, https://sisweb.tesouro.gov.br/apex/f?p=2501:9::::9:P9_ID_PUBLICACAO:27710 , page 8). This Brazil convention is unusual. I'm mentioning it to illustrate that assuming the more common convention might lead to different results. it's safer to explicitly state your assumptions. Many economists are fond of saying "ceteris paribus" without thinking through what that means.
Suppose then that the same positive cash flow amount $C$ can be paid at time $t_1$ or at time $t_2$, $t_1 < t_2$, and that rather than quoted yields (which might not be comparable), you're given discount factors for future cash flows $d_{t_1}$ and $d_{t_2}$.   Which choice has higher present value: $d_{t_1}C$ or $d_{t_2}C$? That depends on whether $d_{t_1} > d_{t_2}$. Many older books implicitly assume this (i.e. assume that interest rates are positive). This is usually the case, but sometimes people find themselves in a deflationary environment and would welcome an oppostunity to "lend out" $C$ at zero interest rate from time $t_1$ to time $t_2$.
Answer: The "proof" is simplest for a perpetual bond, where Price = Coupon/Yield.
So an annual coupon of 1 at a 1% yield is worth 100. Pay 0.5 every six months and the same 100 represents a six-monthly yield of 0.5%. (1.005)^2 = 1.0025% compounded annually. Discounted by the same 1% annual rate, the higher frequency will be worth a little more... and the same will be true (to a lesser degree) in any finite-life bond where you DCF these discrete payments.
In reality, most of this will not really affect traded bond prices, because of clean-vs-dirty pricing. On the day after the 6m frequency bond pays its coupon, it will be clean. But anyone trading the 1y equivalent will have that 6m accrued that the seller pays to the buyer. So in reality, it doesn't make any material difference at all.
https://en.wikipedia.org/wiki/Dirty_price
Answer: If coupon rate > yield rate => the more frequent the payment, the higher the bond price
but if coupon rate < yield rate => the more frequent the payment, the lower the bond price
Comment: I need exactly a proof of the relation you quoted. Can you give me a reference?
Comment: @user279687 Actually I came into this conclusion by simply calculating bond prices on an excel sheet and saw this relationship, but when I asked my fixed income professor he said that always increasing payment frequency would lead to an increase in the value of a bond, regardless of if the coupon rate is higher or lower than the yield rate. When I showed him my excel calculation, he rightfully pointed out that when you change the frequency in the excel bond pricing function, it assumes that both yield and coupon would have the same frequency, so it also changes the yield rate.


Difference between natural and organic

Question: For products such as bread, state they are either natural or organic, what is the difference?
Answer: Natural is purely a marketing term, and it is essentially meaningless since it isn't regulated by the USDA (I'm assuming you are in the USA, I can't speak for other countries). Since the term isn't regulated (with the apparent exception of meat), any manufacturer can put it on any (non-meat) product that they want, whether it is actually "natural" or not.
Organic is well-defined by the USDA and places a number of restrictions on the types of pesticides and other chemicals that can be used to grow the crop. For things like meat, the organic label regulates both the drugs that the animal is given as well as the production of the feed.

Certified organic food products are
  regulated by the U.S. Department of
  Agriculture and produced by farmers
  and manufacturers under a strict set
  of rules. But the agency defines the
  term "natural" only for meat and
  poultry. In the rest of the food
  industry, the meaning is largely up to
  the producer.

See: http://articles.chicagotribune.com/2009-07-10/business/chi-natural-foods-10-jul10_1_organics-or-least-chip-popular-horizon-organic-brand-organic-industry-watchdog-group
Comment: There is a certification for "Naturally Grown" also.
Comment: of course "organic" is a massive marketing hoax as well. ALL meat, plant material, etc. etc. is organic matter. There are very few things in our diet that aren't organic matter (salt comes to mind). Independent studies of "organic farms" also constantly find them to be rife with pesticides, herbicides, and all the other stuff they claim not to use.
Answer: Natural
"Natural foods" and "all natural foods" are widely used terms in food labeling and marketing with a variety of definitions, some of which are vague. The term is assumed to imply foods that are minimally processed and do not contain manufactured ingredients, but the lack of standards in some jurisdictions means that the term assures nothing. The term "organic" has similar implications and has an established legal definition in many countries and an international standard. In some places, the term "natural" is defined and enforced. In others, such as the United States, it has no meaning.
Organic
Organic foods are those that are produced using environmentally sound methods that do not involve modern synthetic inputs such as pesticides and chemical fertilizers, do not contain genetically modified organisms, and are not processed using irradiation, industrial solvents, or chemical food additives.
(Information from Wikipedia)
Comment: It's important to note an "organic" certification does _not_, in _any way_ mean food is produced "using environmentally sound methods." It simply means the food is free from certain chemicals during production. It is still possible (and indeed common) to raise organic foods in ways that exploit natural resources--such as slashing and burning rain forests, irresponsible irrigation methods, etc. While I believe "organic" is generally going to be better than non-organic, for the purpose of human health, don't be fooled into thinking "organic" means "completely environmentally-neutral."
Comment: "that do not involve modern synthetic inputs such as pesticides " That's a major flaw, as "organic farms" often use more of those than regular ones. (or used to, the study I saw on it was some years ago, showed 10 times the pesticides on a large sample of "organic" fruit and produce as compared to normal fruit from the same region.
Comment: @jwenting: Even that criticism (while perhaps true) suffers from lack of definition. There are organic pesticides that can be used while retaining the "organic" label.  And (presumably, if not in fact) such pesticides would be safe(r?) than a non-organic pesticide. So having 10x more of a non-harmful substance than a harmful substance isn't really a very interesting statistic.  Of course maybe your study found that non-organic pesticides were indeed being used, but without seeing the actual study, it's impossible to conclude that it means "organic" is meaningless.
Comment: @Flimzy botulism, anthrax, Ebola, are all "natural". While not used as pesticides, there are those who consider human beings to be pests and they work very well against human beings. Just because something is "natural" then doesn't make it safe. Similarly, a lot of things that aren't "natural" are quite safe. The whole "natural pesticide" thing together with "organic farming" is just bunch of balony, pure marketing trickery to fool people into paying excessively high prices for otherwise ordinary (and often substandard) produce.
Comment: @jwenting: I never made the claim that natural == safe. And there's certainly a lot of wiggle room in the terms. But that makes them "pure baloney." "Organic" in particular has a specific legal meaning, and maintaining compliance with that label requires real effort and expense.  As such, the label can be useful--especially to those who actually take the time to understand what it means, and that it isn't some sort of magic bullet.
Answer: From http://www.organicfacts.net/organic-food/organic-food-basics/difference-between-organic-and-natural-food.html

Organic food refers to food items that are produced, manufactured and handled using organic means defined by certifying bodies such as the United States Department of Agriculture (USDA) under its Organic Food Products Act. Natural food, on the other hand, generally refers to food items that are not altered chemically or synthesized in any form. These are derived from plants and animals. Thus a natural food item is not necessarily organic and vice versa.

as far as I understand it, there's really no clear definition to either of these two terms and they're mostly overused by companies to sell you products.  I believe the use of "Natural" is a little more devious. For instance, I just bought some "Natural Style" apple juice the other day.  I'm sure it's just as processed and pasteurized, it's just a slightly different flavor/color.
Comment: "Natural Style"?  That's kind of like those movies that are "inspired by actual events"...  In other words, a complete work of fiction except with the names of actual places and people...
Comment: @GalacticCowboy See also "juice beverage".
Comment: I wouldn't say that there is no clear definition to organic in the US.  There are actually quite strict certification procedures that you must undergo before you can legally claim that any food you sell is organic.  For instance, because I use 10-10-10 fertilizer in my garden I cannot sell my produce in a farmers market as organic.  These restrictions span across both animal and vegetable products.  You can find all the details on the government website, including the text of the actual bill in Congress that enacted these regulations [here][1].

  [1]: http://www.ams.usda.gov/AMSv1.0/nop

Difference between natural and organic


Why does a DFA have multiple final states?

Question: I am taking a course on programming language design and we got to the DFA part. It is known to be formally defined by a 5-tupple but they did not make it very clear to us why a DFA can have multiple final states. I know that the languages that it can accept are involved, but nothing else.
Comment: The answer, strictly speaking, depends on the definition of a FA you're using. While they're equivalent, some authors say a FA must have at most one final state, while others allow them. As I said, it makes no real difference which you use.
Comment: Not sure why this was downvoted, it's a great conceptual question.
Comment: Relevant here: "[Why do DFAs with a single final state have less power?](https://cs.stackexchange.com/q/101111/4287)", and "[Show that for any natural number n, there is a regular language that is not recognized by any DFA with at most n final states](https://cs.stackexchange.com/q/30718/4287)"
Comment: Just to be sure, are you asking why it _should_ be defined to have multiple final states? That's how we're interpreting the question.
Answer: A DFA is a machine that reads in its input left to right, and, while reading, keeps track of its internal state. At the end, it has to decide whether to "accept" or "reject" the input based only on whatever internal state it has at the end. The final states are used to indicate which internal states should inform the machine to accept.
The reason we need to have multiple final states, then, is because we might want to accept the input in multiple different scenarios. Here is a simple example. Suppose we want to design a machine that accepts if the input is either ho, hoho, or hohoho (so we want to accept, in total, three possible input strings). Then the "state" of the machine can keep track of what letters we have seen so far: we have 7 states for [nothing], h, ho, hoh, hoho, hohoh, hohoho. If we get a letter that isn't going to be one of these strings (like if the input is haha or asdf), we need a different state to remember that the input was bad, and we can call that state [bad input]. So in total we have 8 states.
Now in this example, we want to accept three different strings: ho, hoho, and hohoho, so we need all three of those states to be final. It turns out that it would be impossible to accept these three strings if we have to have only one final state.
All states (8): [nothing], h, ho, hoh, hoho, hohoh, hohoho, [bad input]
Final states (3): ho, hoho, hohoho

In summary, multiple final states gives us the ability to accept multiple different possible patterns in the input. The above is one example of that, but there are many other examples where it is useful.
Comment: However, the longer answer is that designing such a DFA would be possible if you assume that all input strings are terminated with a special "end of input" symbol, like null-terminated strings. But in the usual definition of a DFA, this representation of strings is not used.
Comment: In this case it's very easy to prove that two different accepting states are needed: hoho and hohoho must both end in an accepting state. And they can't end in the same state, because processing ho from the state of hoho must end in an accepting state (because hohoho is in the language), but processing ho from the state of hohoho must end in a rejecting state (because hohohoho is not in the language. So we have two inputs that must end in different accepting states.
Comment: @kelalaka No that is not possible. In this example there is no way to have only one final state because the states for `ho` and `hoho` need to be different.
Comment: Can't we design a big DFA that only one final state that has equal functionality with the multiple ones?
Answer: Consider an arbitrary nondeterministic finite automaton.
If it has multiple final states, you can create an epsilon transition from all of the final states to one common final state, remove the "final state" mark from all of the previously final states so that you have only one final state. So, a nondeterministic finite automaton can very well work with just one final state.
However, if you explode a nondeterministic finite automaton into a deterministic finite automaton, you'll find that you no longer can have epsilon transitions. The states of the exploded deterministic finite automaton correspond to sets of states in the nondeterministic finite automaton.
You will find that you need to mark a state as "final state" if at least one of the NFA states in the set is the final state. There may be multiple such states.
So, in summary: an NFA can very well work with just one final state. A DFA can't, unless you want to restrict DFAs arbitrarily. By arbitrarily restricting DFAs, you are creating a situation where there are NFAs that cannot be converted to DFAs, and that there are regular expressions that cannot be accepted by any DFA.
Answer: Let me provide a characterization of what languages DFAs with a single accepting state can accept.
Proposition. A language $L$ over $\Sigma$ is accepted by a DFA with a single accepting state if there exist two regular prefix codes $A,B$ such that $L = AB^*$. Furthermore, this representation is unique, assuming $L \neq \emptyset$ and $\epsilon \notin B$.
(A prefix code is a set of words, none of which is a prefix of another one. It is regular if as a language it is regular.)
Proof. Let $A$ be the language of words which move the DFA from its initial state to its final state without transitioning through the final state (if the initial state is also final, $A = \{\epsilon\}$), and let $B$ be the language of non-empty words which move the DFA from its final state back to itself, again without transitioning through the final state.
The languages $A,B$ are clearly regular. To see that they are prefix-free, suppose to the contrary that $x,y \in A$, and $x$ is a proper prefix of $y$. Thus when reading $y$, the DFA passes through the accepting state upon reaching $x$. The case of $B$ is similar.
In the other direction, consider a minimal DFA for $A$. All words in $A$ are equivalent with respect to the Myhill–Nerode relation. Indeed, if $x,y \in A$ then $x\epsilon,y\epsilon \in A$ by $xz,yz \notin A$ for $z \neq \epsilon$ since $A$ is prefix-free. Thus the minimal DFA contains a unique accepting state. Similarly, the minimal DFA for $B$ contains a unique accepting state. Merging the accepting state of the former DFA with the initial DFA, we get the desired DFA.
Finally, let us show that the decomposition is unique. Given $L = AB^*$, we an extract $A$ as the set of words in $L$ which have no proper prefix in $L$. Taking any $w \in L$, we can extract $B$ as the set of words in $w^{-1} L$ which have no proper non-empty prefix in $w^{-1} L$. (This step fails if $A = \emptyset$.) $\square$

In particular, if $L$ contains two words $x \neq y$ such that $x$ is a prefix of $y$ then $L$ is infinite (since $B$ must contain a word other than $\epsilon$). This shows that $\{ho,hoho,hohoho\}$ requires more than one accepting state.
From Myhill–Nerode theory, it is known that the minimal number of accepting states equals the number of Myhill–Nerode equivalence classes of words in the language. In the example $\{ho,hoho,hohoho\}$, each word is in its own equivalence class, so exactly three accepting states are needed. (With some work, it should be possible to identify a combinatorial parameter which determines the minimal number of accepting states in any finite language.)
Comment: There seems to be an error in the proposition: $ab^*a$ is accepted by a DFA with one final state, but is not of the given form. More generally any language with a "visible" end of string will be accepted by a DFA with one final state: e.g. $\# L \#$ for any regular language $L$ over $\Sigma \setminus \{\#\}$.
Comment: Right. That's what happens when a proof is not spelled out... Hopefully the current version is correct. I replaced "finite" with "regular".
Comment: +1. Just one other thing: I think the assumption $\epsilon \in B$ is not what you want, since that implies that $B = \{\epsilon\}$. I think you want $\epsilon \notin B$ instead (edited to fix).
Comment: I guess there is another edge case where $L$ is empty. Then $A$ must be empty but there are many possible choices for $B$. The case $L$ finite and nonempty corresponds to $B = \varnothing$, so that is OK.
Comment: Since $S^* = (S \cup \{\epsilon\})^*$, the exact status of $\epsilon \in B$ doesn't matter.
Comment: It does matter, because you have assumed $B$ is a prefix code. This implies that if $\epsilon \in B$ then $B = \{\epsilon\}$.
Comment: Right, good point.


Can Super Saiyan God (Red) Kaio-ken be made just like Super Saiyan God Super Saiyan (Blue) Kaio-ken?

Question: In the last manga, Goku is able to transform in Super Saiyan God Red on his own, without the other 5 Saiyans surrounding him in a ritual. My question is, in this transformation, can he use the Kaio-ken on top of it, just as he used it with the Super Saiyan God Super Saiyan transformation (Super Saiyan Blue)?
Comment: @MichaelMcQuade in the anime he does to try and defeat Hit, though in the end he bails out, and immedatly his body twists and distorts presumably because of kaio ken, leading to a short filler arc where he cant control his Ki.
Comment: When does he use Kaioken as super saiyan blue?
Comment: Perhaps consider changing the tag - this question isn't about the whole Dragon Ball series, just Dragon Ball Super (or just after DBZ)
Answer: Your question is a tricky one, my friend. It hasn't been covered in the anime or the manga as to whether or not that is possible, but theoretically it should NOT be.
Why? Because in the anime which has already been declared canon ("somewhat..."), it has been stated that Kaioken on top of SSB is allowable because it is used on god-ki under perfect ki control.
SSR does not have perfect ki control which is why it can only be done via ritual, and also why Vegeta does not have SSR form.
Arguably since the manga and the anime deviate whereas spoilers below for anyone who isn't caught up...

 In the battle between Goku and Hit, two different outcomes are portrayed. In the anime, Goku uses Kaioken x10 while in SSB to enable him to overpower Hit's time-skip ability. Doing so makes him unable to control his ki for a period of time, forcing him to warp into the wrong places and leaving him unable to even fly correctly. Now in the manga, Goku transitions between SSR and SSB, throwing Hit's timing out of whack and eventually defeating him. So this brings in two hot topics:

 Is SSR still usable without the ritual due to the zenkai boost?
Is Kaioken usable compounded with SSB? Which one is the canon here? One is true and the other has to be false, unless for some strange reason both are true.

Kaioken on SSB may not even "technically" be real due to the anime only being partially canon.
TLDR: Theoretically no, and with what has currently been seen in the anime and manga as of June 27, 2016, no. Is it possible? Yes.
Comment: In the last manga SSR is done without ritual by Goku , did you mean in the anime it cant be done without ritual?
Comment: Yes that is what I wrote. In the manga SSR no ritual is cannon. And in the anime ssb kaioken x10 is cannon. One of these is false but we don't know which yet.


Compatibility with 105 shifters

Question: Can I use Deore RD-T610-SGS derailleur on my road bike with 105 shifters, it seems like cable pull isn't right. Shifters are on 2007 Specialized Roubaix compact.
Comment: Sheldon brown's site contains a lot of information on compatability - another issue is cassettee - so prob easiest to start there
Answer: Shimano 10 speed mountain rear derailleurs or 11 speed road derailleurs work with Shimano 11 speed road shifters.
Shimano 7,8,9,10 speed road and 7,8,9 speed mountain derailleurs work with Shimano 7,8,9,10 speed road shifters in terms of cable pull.
Answer: Actually, I use a 9-speed mount derailleur (deore xt) on a 10 speed cassette (11-32) with a 10 speed road shifter (105) and a triple (50/36/30).  The cable pull is fine.  The capacity is just OK.  It took some b-screw adjustment to get it working well.
It turns out there are many people doing the same thing, especially on tandems.
This fits what you said - but it is notable that one can still run a 10 speed mountain >cassette< with a 10 speed road shifter.

Compatibility with 105 shifters


How does absorb elements work with pre-existing resistances

Question: So I've looked around and can't find an answer that quite fits what I'm wondering. For example, if I were to already have fire resistance, and I get hit with a red dragon's fire breath, would casting absorb elements halve the damage I take(effectively making it 1/4 damage) or not reduce damage at all because I already have 1 source of resistance?
Answer: You either have resistance or you do not, different sources of the same resistance type do not stack.
Resistance and vulnerability (P197 of the PHB)

Multiple instances of resistance or vulnerability that affect the same damage type count as only one instance. For example, if a creature has resistance to fire damage as well as resistance to all nonmagical damage, the damage of a nonmagical fire is reduced by half against the creature, not reduced by three-quarters.
Answer: The spell functions as normal, but offers no defensive benefit.
You either have or do not have resistance. Having it from two different sources has no effect, unless some effect specifically ignores resistances provided by one source or not another - I am not aware of such an effect.
That said, casting the spell will still cause you to deal the extra damage, which may be significant.
Comment: It would be good to support this with a quote from the rules, like the one in the other answer


How to install Windows 7 using an external display?

Question: I have a Sony Vaio VPCF115FM.
Through a lot of research online, I've come to find out that this laptop has external video ports (VGA & HDMI) that only work once the operating system loads the drivers for the nVidia graphics card. Therefore, you cannot see any of the boot process such as BIOS, POST, etc.
My problem is, the laptop display is cracked and I can't afford $200 for a screen (cheapest I can find) and I'm unemployed at the moment. Recently, my hard drive died, so I'm trying to reinstall the operating system (Windows 7). But since the nVIdia driver is not included in the install disk, I can't see antything on the screen.
Possible solutions  I could think of:

WindowsPE (e.g., Hiren's Boot Disk): I could use something like Hiren's because it contains a easy installer for Windows OS's. But again, no video graphics driver.
How can I place a video driver in Hiren's, or even create a new PE with the driver included?
Figure out which keys I should press, in the correct order, to install the OS, reboot, and download and install the driver. (ugh)

What else could I try?
Answer: You could look in to unattended install mode for windows.


Why did Greek Olympic games take place every fourth year?

Question: I was wondering why Greeks chose to have Olympic games every four years. Now, since we usually every fourth year is a leap one, it makes sense; but the reform of the calendar which stated this is due to Julius Caesar, and besides (see here) Greeks had a lunisolar calendar based on Metonic cycle, and a very good appoximation of the tropical year came only with Hipparcus, who lived in the 2nd century BC. I naively thought that a 5-year period should have been more logical, but maybe they had some scientific reason to choose a 4-year period. Does any evidence exist?
Comment: According to ancient tradition, the games were established in 765 BC, though modern scholars disagree. The approximate length of the year as 365 1/4 days was known very long ago, long before introduction of Julian calendar. Whether this 1/4 is related to 4 year period is a good question but probably has no answer within our current knowledge.
Answer: It is unknown why the 4 year period, a.k.a. the olympiad, was chosen. Most of the writings concerning the origins of the games come from 2nd century AD historians, nine centuries after the fact, and are largely mythological. According to one of them, Pausanias, "dactyl" Herakles and his four brothers, Paeonaeus, Epimedes, Iasius and Idas, raced at Olympia to entertain the newborn Zeus, who then crowned the victor with an olive branch, which became a peace symbol. Each year of the olympiad (inclusively) is to celebrate each brother. This is most likely a late fable invented to "explain" traditions the true source of which was forgotten. What little can be plausibly extracted from the myths is that the games were tied to worship of the gods, and were intended to promote and maintain peace and cooperation across Greece.
The only known astronomical connection is that the games began on the full moon closest to the summer solstice, which marked the start of a new year. The date was somewhat altered after the introduction of the Metonic cycle c. 432 BC. The Metonic cycle is close to a common multiple of the solar year and the synodic lunar month, and it is 6,940 days, about 19 years. Dividing gives 365 + 1⁄4 + 1⁄76 days per year, which comes close to rounding up the fraction every four years. Whether this played a role in the choice made earlier one can only speculate. If there was something tied to gods that all Greeks could agree on it would be what is seen in the heavens. We do know that after three centuries Greek historians started using the olympiad as a universal interval for reckoning time independently of individual conventions in city-states.
Answer: The estimate of the length of the tropical year and the synodic month by Meton, Hipparchus and others has no bearing on the system of four-year Olympiads. The use of a 365-day year with a leap day every four years was introduced by Julius Caesar in the first century BC. A similar calendar had previously been decreed in Egypt in 238 BC, but never actually implemented. The dating of events according to Olympiads can be traced back at the latest to Thucydides (5th century BC).
Comment: Nitpick: The Ptolemies created a solar calendar with a day added every four years in the third century BC.  It doesn't seemed to have been widely used, but it was probably what inspired Julius Caesar's reforms when he visited Egypt.  So there was at least one such calandar in existence before the Julian.
Comment: The 20th paragraph of the Canopus Decree instructs Ptolemies subjects to obey the new calendar.  http://www.reshafim.org.il/ad/egypt/texts/canopus_decree.htm
Comment: You are right and I have corrected this. The "Canopus" calendar was decreed in Egypt in 238 BC. However, all of the available evidence indicates that it was never actually implemented.
Comment: Most recent discussion: Sacha Stern "Calendars in antiquity", Oxford 2012, pp. 137-142.


Is there a .NET library for standardizing my images / documents to PDF?

Question: I need to be able to import and process a variety of different images and documents. I need a tool or library that will ingest the file and perform OCR if necessary, but save it out as a standardized PDF file for archiving purposes (PDF/A). Is there a tool or .NET library that can achieve this? If the document is already searchable, it should not OCR it again.
Answer: You may want to consider trying the Leadtools SDK. Their DocumentConverter is designed especially for this type of workflow. You can take any document or image format, vector based or raster, and convert to any other document or image format, and OCR is performed automatically based on your settings. Below you can find a quick snippet for converting a directory of various files to PDF documents in another directory. Just as a disclaimer, I work for the vendor of this product.
using (DocumentConverter documentConverter = new DocumentConverter())
{
    string inputDirectory = @"C:\temp\input files";
    string outputDirectory = @"C:\temp\output documents";
    string[] inputFiles = Directory.GetFiles(inputDirectory);

    // Required for document output
    var documentWriter = new DocumentWriter();
    documentConverter.SetDocumentWriterInstance(documentWriter);

    // Optional for Raster -> Searchable Vector
    var ocrEngine = OcrEngineManager.CreateEngine(OcrEngineType.LEAD);
    ocrEngine.Startup(null, documentWriter, null, null);
    documentConverter.SetOcrEngineInstance(ocrEngine, true);

    // Look through each file in the input directory
    foreach (var filename in inputFiles)
    {
        // Create a DocumentConverterJobData that holds the necessary information
        var jobData = new DocumentConverterJobData();
        jobData.InputDocumentFileName = filename;
        jobData.DocumentFormat = DocumentFormat.Pdf;
        jobData.OutputDocumentFileName = Path.Combine(outputDirectory, Path.GetFileNameWithoutExtension(filename) + ".pdf");

        // Create a job with the necessary jobData and execute it
        var job = documentConverter.Jobs.CreateJob(jobData);
        documentConverter.Jobs.RunJobAsync(job);
    }
}

Comment: Hello @JClark742, thank you for your answer. I have a couple follow up questions:
Is this a commercial library? If so, where can I see pricing and can I try it for free before buying? Does this work cross platform via .NET 5? Is there a Nuget library I can use?
Comment: LEADTOOLS is a commercial library that you can download and try for free here: https://www.leadtools.com/downloads. You can also find our NuGet packages here: https://www.nuget.org/packages/Leadtools.Document.Sdk/. This is supported on .NET and you can find our basic pricing outline here: https://www.leadtools.com/sdk/product-overview.
Answer: Syncfusion's Essential PDF (.NET PDF library) supports OCR by using the Tesseract open-source engine. A scanned paper document containing raster images is converted to a searchable and selectable document with a few lines of code. Please refer to the below links for more information,
UG: https://help.syncfusion.com/file-formats/pdf/working-with-ocr/dot-net-framework
KB: https://www.syncfusion.com/kb/9144/how-to-convert-scanned-image-to-searchable-pdf-by-processing-ocr
NuGet information: https://help.syncfusion.com/file-formats/pdf/nuget-packages-required#pdf-ocr
Please refer the below code snippet to OCR a PDF document and save with PDF/A1b conformance.
using Syncfusion.OCRProcessor;

using Syncfusion.Pdf.Parsing;

using System.IO;

static void Main(string[] args)

    {
        string path = Path.GetFullPath(@"../../Tesseract_bin/x86/");

        using (OCRProcessor processor = new OCRProcessor(path))

        {
            processor.Settings.TesseractVersion = TesseractVersion.Version4_0;
            //Load a PDF document

            PdfLoadedDocument lDoc = new PdfLoadedDocument("../../Region.pdf");

            lDoc.Conformance = Syncfusion.Pdf.PdfConformanceLevel.Pdf_A1B;

            //Set OCR language to process

            processor.Settings.Language = Languages.English;

            //Process OCR by providing the PDF document and tesseract data, and enabling the isMemoryOptimized property

            processor.PerformOCR(lDoc, @"../../LanguagePack/", true);

            //Save the OCR processed PDF document in the disk

            lDoc.Save("Sample.pdf");

            lDoc.Close(true);

        }
    }

We have also provided the support for PDF to PDF/A conversion in our Syncfusion PDF library, please refer the below link,
PDF to PDF/A: https://help.syncfusion.com/file-formats/pdf/working-with-pdf-conformance#pdf-to-pdfa-conversion
More PDF Examples: https://ej2.syncfusion.com/aspnetmvc/PDF/Default#/material
The whole suite of controls is available for free (commercial applications also) through the community license program if you qualify. The community license is the full product with no limitations or watermarks.
Note: I work for Syncfusion.
Regards,
Gowtham


How can I start learning mathematics for machine learning?

Question: I am an Android programmer. Now, I would like to learn machine learning. I know it requires a mathematical background, like statistics, probability, calculus and linear algebra. However, I am a bit lost. Where should I start from? Can someone provide me a road map for how to learn the mathematical background required for machine learning?
Answer: You should begin from Dr Andrew Ng machine learning course on Coursera. It's probably the most popular course for newcomers in machine learning. It's a free course.
You should also grab "Elements of Statistical Learning" ebook PDF. It's a free book.
You may want to focus on:

Regression
Cross validation
Bias-variance tradeoff
Decision surface
Gradient descent

And more...
Answer: Some of the fundamental mathematical concepts required in ML field are as follows:

Linear Algebra
Analytic Geometry
Matrix Decompositions
Vector Calculus
Probability and Distribution
Continuous Optimization

A very recent book availble at Mathematics for Machine Learning covers all these aspects and more.
Answer: If you are interested to deepen your statistical concepts before diving into machine learning, i would recommend Introduction to Statistics: Descriptive Statistics course in edX
where you'll learn

The fundamental concepts and methods of statistics
How to intepret graphical and numerical summaries of data
Understand the reasoning behind the calculations, the assumptions under which    they are valid, and the correct interpretation of results

The link for course is edX
This will definitely clarify your stat background with added benefit of certification.


Did Common Brittonic use /ṽ/?

Question: I heard on the Wikipedia article for Sindarin (which I admit is far from being the best source) that Common Brittonic, like Old Irish, had a nasalized v sound ṽ. Is this true? If so, are there any other language that use this sound? I'm sorry if this isn't a valid question.
Comment: Which conception do you mean? The Old Irish one, or the Brythonic one? The Old Irish one, I assume, was just because in Modern Irish, the bilabial fricative has disappeared, and the broad and slender allophones are [v] and [w] in most dialects ([vʲ] and [vˠ] in others), so [v] is present nowadays. It's also a lot easier to type, so I think it was just used as a phonemic shorthand that wasn't necessarily intended to say anything about the phonetic reality of the sound, but was then taken too literally and broadened out. For the Brythonic, I don't know, but there are probably reasons.
Comment: It's often stated that Old Irish used [ṽ], but there's no proof that this is actually the case, and when you see it, it's usually just repeated uncritically. Given the later outcomes of all the labial fricatives, it's more likely that the sound was actually (palatalised and non-palatalised) [β̃] instead. Evans' _Grammar of Middle Welsh_ (best I've got available for Brythonic) says a bilabial realisation is also likely for earlier stages of Welsh; I don't know enough about Brythonic to say much beyond that, unfortunately.
Comment: Although I will just add that people like Peter Schrijver and Stefan Schumacher (perhaps also Kim McCone? Can't remember offhand) write the 1sg verbal ending in Common Brythonic as _-ǖμi_, which _may_ indicate that they consider it to have been [β̃] rather than [ṽ], but definitely indicates that they don't just consider it [v].
Comment: Neat! where do you think that conception came from?
Answer: This phoneme /ṽ/ appears to be common to both Common Brittonic and Old Irish, and shows the difficulties that the contemporary scribes for Old Irish had with notating nasalisation. As of January 2021, Wiktionary transcribes it for Common Brittonic as /β̃/ but Old Irish with /ṽ/. The difference between the two being merely a notation difference is mentioned in Stifter's Sengoidelc: Old Irish for Beginners:

/μ/ is pronounced like /β/, but with a nasal quality. In other publications you may find this transcribed as /ṽ/.
/β/ is a labial sound as in Latin Vergilius. In other publications you may find this transcribed as /v/.

However, Gillies (2009:435) sees this as stages in diachronic change:

[μ] > [ṽ] > [v], [β] > [v]

It was by no means a rare marginal phoneme: it was used in words as common as *nemos "sky" and *temeslos "darkness". Its reflex remains a important part of the morphophonemics of the modern Celtic languages, occurring whenever lenition (soft mutation / séimhiú in Irish / treiglad meddal in Welsh) operates on the phoneme /m/.
Owing to the conservative nature of Irish orthography, it corresponds quite well to the spelling mh in Irish and Scottish Gaelic, e.g. teimheal. In Modern Welsh, it is mostly written with w or f, but a lot of these have mu in Old Welsh. Breton uses v for the form after lenition, although it frequently uses the digraph ñv, indicating nasalisation of the preceding vowel; older forms vary between fv, n, and nv.
Nonetheless, the modern reflexes of this consonant across Celtic languages vary between /w/ and /v/ (palatalised or velarised); only in Breton is the nasalisation retained, and even then, I'll let you all be the judge of neñv and teñval, and to what extent the spelling reflects modern phonetics versus historical etymology.
There have been studies about the nature of nasal fricatives; one 2016 paper states how they are "unusual, maladaptive articulations". More relevant to this question, there has been work done understanding to what extent mh is different to bh and ph in Modern Irish and Scottish Gaelic. This is currently under investigation: a 2015 paper claims incomplete merger in Scottish Gaelic, implying some marginal distinction, and also cites two languages which have been claimed to have [ṽ]: Umbundu and Coatzospan Mixtec; the authors conclude it is phonetically a form of vowel nasalisation that spreads, turning the fricative into more of an approximant. On the other hand, one 2020 study concludes that there is no distinction between bh and mh, and that there is insufficient evidence for any nasalisation.

Did Common Brittonic use /ṽ/?


Removing GUI of Raspberry Pi B+

Question: I would like to ask how to open a Raspberry Pi in terminal mode only? Right now i want my Raspberry Pi to just autorun a Python script after plugging the power supply. Thanks for the answers guys.
Answer: From the command line open the raspi-config script:
<code>sudo raspi-config
</code>
Using your up down arrows select option 3:
Boot Options
Then select Option 1:
Desktop/CLI
Select either option 1 or 2:
Console or Console Autologin
Then Click (use the tab key):
OK
Finally click:
Finish
and reboot to test.
These settings are also available from the GUI preferences menu.
Comment: Comments arfe not for asking unrelated questions. If you can't finfd the answer by searching either google or this site then ask a new question.
Comment: if my raspberry disable the GUI, how can i go back to GUI?
Comment: The same way except you choose desktop or desktop autologin instead of console.
Comment: sir can i ask how can i determine my Raspberry Pi B+ if its Raspbian Wheezy or Raspbian Jessie?

Removing GUI of Raspberry Pi B+


Is there anything wrong with leaving toilet tank below waterline?

Question: In troubleshooting a problem with recurring flushing (turned out to be a worn out flapper) I lowered the tank water level to about an inch below what the manufacturer marked as the waterline. Flushing seems to work fine - plenty of force, refills, fine and the flapper is fixed. I'd like to conserve water by leaving the water line where it is now, but will I be causing some kind of problem if I do?
Answer: As a volume reducer, people have put two or three bricks in the tank to conserve on the quantity of water used per flush.
Being down by 1 inch of head on the water level isn't much to worry about.
As long as it flushes the contents either way, you're fine.
Comment: Someone used some drink bottles filled with water in mine, and attached them with rubber bands. Worked well enough until the one of the rubber bands broke while I was away and the bottle hung up the float preventing it from filling, and I got a frantic/confused text from my wife to the effect of "Eww! Someone left a strawberry milkshake in the back of our toilet and now the toilet is broken! Help!"
Comment: Heh, rubber bands have a way of doing that.


Changing attachment urls?

Question: How can I change the format of attachment page urls from /[post-url]/[attachment-name]/ to /media/[attachment-name]/? I understand that I can override the output of get_attachment_link via the attachment_link filter, but I guess I need to change the redirect structure so WordPress knows how to handle these urls?
Answer: You can do the following:
/* add new rewrite rule */
function attachment_rewrite( $wp_rewrite ) {
    $rule = array(
        'media/(.+)' => 'index.php?attachment=' . $wp_rewrite->preg_index(1)
    );

    $wp_rewrite->rules = $rule + $wp_rewrite->rules;
}
add_filter( 'generate_rewrite_rules', 'attachment_rewrite' );

/* redirect standard wordpress attachments urls to new format */
function redirect_old_attachment() {
    global $wp;

    if( !preg_match( '/^media\/(.*)/', $wp->request ) && isset( $wp->query_vars['attachment'] ) ) {
        wp_redirect( site_url( '/media/' . $wp->query_vars['attachment'] ) , 301 );
    }
}
add_filter( 'template_redirect', 'redirect_old_attachment' );

Comment: where do we add the above code, do we add it in functions.php or rewrite.php or links-template.php
Comment: add it to your theme functions.php file
Comment: Where can I find / update the `'index.php?attachment='` handler? I want to use my own handler to resolve files, filter only for a specific user(s) & etc

Changing attachment urls?


Do both the Chatan and kallah need to be present in order to say sheva brachot?

Question: Whether it be two or seven blessings, do both the bride and groom need be present for sheva brachos?
Comment: @Mennyg indeed, that seems to be the custom, but Rav Ovadia Yosef explicitly says that it is not necessary. (Yabia Omer 9:2)
Comment: I don't have a source, but by every single sheva brachos I've been to, they made sure the kallah was on the mens side of the mechitzah...
Comment: Thanks menny, but I believe that is due to it being, in the words of chacham Ovadia z'tl "a proper and good minhag." In the yalkut yosef there are multiple instances where it seems the Halacha included both bride and groom, but in hazon Ovadia (Shabbat,chelek bet sorry I'm sourcing from memory) it seems that only the chatan need be present...
Comment: @Matt could be a difference in opinion between sfardim and ashkenazim. I have never been to a sfardi sheva brachos, but every ashkenazi one I've been to, the kalla was brought in. Even by big chassidic rebbes, where she ends up being the only woman among thousands on chassidim
Comment: It's important to realize Rav Ovadia says the *presence* of the Kallah is necessary; seating her with the men is not.
Answer: The Yam Shel Shelomo (Kesuvos 1:20) writes that the brachos are primarily directed towards the chosson, and so if the bride is not present then they may still make all seven brachos, as long as the groom is there. The China v'Chisda on Kesubos (vol. 1, p. 113b) agrees, though he quotes the Ritva as holding that both the bride and groom must be present. He also quotes (later, vol. 3 p. 272b) from others that even if the groom was not present for some reason, but the meal was still prepared in honor of the couple, some say that Sheva Brachos can be made, and apparently that was the custom in Salonica.
Rav Ovadia Yosef in Yabia Omer 6:9:1-2 brings many sources (כדרכו) as to what to do in such a case, and concludes that the Shulchan Aruch appears to hold like the aforementioned Ritva. Therefore, both the bride and groom must at least participate in the meal, and although strictly speaking the bride can be in a different room, it is best for her to be brought in for the brachos (see also Yalkut Yosef Sova Semachos 1, 16:3, 16:8)
Apparently such a case occurred in 19th Century Nikolsburg, where the groom left for a business trip into his Sheva Brachos week. This case is discussed in both Teshuvas Mahari Asad (no. 12) and Maharam Shik (no. 90), who both believe that Sheva Brachos should not be made in such a case.
Comment: copied from [here](http://judaism.stackexchange.com/a/81152/5083)
Answer: According to many contemporary Poskim - Rav Ovadia (Yabia Omer vol. 6 Even HaEzer 9), Rav Mordechai Eliyahu ("Hilchot Shidduchim and Chatunah" by R' Shmuel Eliyahu), Rav Moshe HaLevi (Birkat Hashem (vol. 4 page 246)), and the Tzitz Eliezer (vol. 13 Siman 99) - if the Chattan and Kallah were both present and ate bread at the beginning of the meal, the guests may recite Sheva Berachot, even if one or the other left in the middle. If, however, one of them was not present at the beginning or didn't eat, Sheva Berachot may not be recited. See also Shalmei Simcha page 323, 355.
Rav Vozner holds that although it's ideal for the Kallah to hear the Berachot, if she is not present during the Seudah, Sheva Berachot may still be recited if she feasts with her entourage separately and then comes with them to Birkat HaMazon. It's questionable if they may do so if she doesn't enter the room, even if hears the singing from outside. (Shevet HaLevi vol. 8 Siman 281)


What to look for in buying laminate flooring

Question: We are beginning to look at replacing the floors in our home and are considering laminate flooring. We are wondering if there is a difference in type and quality, especially when pricing is concerned. For example, the flooring at Lowe's is considerable more expensive than at Sam's Club; should I be worried that the lower cost flooring is a lesser quality? Are there other considerations besides price?
Comment: Most products will have an AC-# rating. This is a European durability rating.  Stay away from 1 & 2 altogether. 3&4 are fairly easy to find. 3 would be ok for a bedroom, and 4 for hallways and living rooms.  5 is industrial grade, and you'd use it for high traffic retail/banking areas..
Answer: Great question! My wife and I were examining laminate flooring a little while ago too. Not all of them are alike -- here are some things to consider.

Check the warranty. Cheaper laminate will usually have a shorter warranty with more conditions (e.g. 10 - 15 years only protecting factory defects).  More expensive laminate will usually cover more conditions for a longer time (e.g. 25 years+ covering factory defect, normal wear and tear, fading, staining, denting and water resistance).  Keep in mind that these are examples -- every manufacturer is different.
Find out details of how a sample is made A lot of laminate flooring is now treated with Aluminum Oxide which protects it against scratching and denting. More expensive laminate may have more coatings.  If you're expecting heavy foot traffic or have animals with nails, you might want to take it into consideration.  For answers to questions like this, you might need to contact the manufacturer directly.
Thickness varies Laminate thickness can vary anywhere from 5mm to 12mm.  The thicker laminate can feel more stable and supposedly be less likely to have problems with humidity changes.
Joint integrity varies Not all laminate flooring interconnects in exactly the same  way.  Some joint connections can withstand weight and water leaks better than others.  Name-brand manufacturers claim to have more experience with this. Be sure to check how the pieces fit together.

-M
Comment: Just for a small clarification- one can actually find 5mm and 6mm laminates as well.  In addition to stability and strength, I've found thicker laminate is easier to snap into place (less flex).
Comment: @markd Thanks for pointing out the thickness error.  Corrected. =)
Answer: I can add one other option from my own experience as a first time laminate buyer/installer.
I'm in a rental where "anything goes" - it's an open floorplan but for the bedroom and bathroom.  It came with horrid (and asbestos-containing) floor tiles.  I eventually decided to buy the cheapest laminate flooring I could find.  I covered an area of about 550 SF and laminate was actually the cheapest option compared to everything else I could find (I'd even considered epoxy paint).
First thing to note is that Lowes and HD have a pretty small selection and even their "cheap" stuff is expensive.  Google found me Lumber Liquidators and I just waited until some of the 6mm stuff fell below $0.60 SF.  It had fairly good reviews (most complaints were about installation issues, which I didn't encounter, being a reader of directions and such) and I was allowed to try to damage the sample in the store.
So in short, I suppose my answer is this - from what I could see, the differences in quality seem to have more to do with ease of installation and appearance than overall durability.  My $0.59/SF flooring shows no signs of wear after a year (and two dogs).  I've tried to damage some extra pieces with varying success - scraping a key does nothing, a sharp nail does nothing, but really gouging at it with a sharp screw can leave a mark.  I suspected as much as I went through 4 circular saw blades cutting each end piece.  The coating seems exceptionally tough and so far I see no issues with the adhesion of the coating to the underlying fiberboard, nor did I see any signs it was not well bonded when cutting it (I never saw the top layer separate from the board).  The joints seem to be holding up, but are slightly visible, perhaps the high-end laminate has tighter tolerances in manufacturing.
Bottom line, if you're looking to spend less than $2.50/SF or so, go with something extremely cheap from a place other than HD or Lowes.


How can I build a shed in two halves and join them without the roof leaking?

Question: I am building a shed and I need to build it in two halves so I can take it off the foundation if I need to. The problem is that due to the dimensions, I have to split it in such a way the split line goes across the roof perpendicular to the ridge. The fact that I will be using wooden shakes makes this even harder. What can I do to keep it from leaking?
Comment: Maybe make it three pieces, one of which is the whole roof.
Comment: What about installing the roofing after you've joined the two halves?
Comment: How big is your shed?
Answer: If the two halves of the shed are built to be structurally sound while separate, then there is no reason that each roof can't be built slightly asymmetrically so that one overlaps a portion of the other to provide weatherproof protection, like this:

Some tweaking of the interface would be needed to make it practical and convenient, but the basic idea would be to build it so there is at least 6 inches of overlap where the higher one covers the lower one.
Comment: From the question: _the split line goes across the roof perpendicular to the ridge_. This looks like it's along the ridge.
Answer: If you are not attached to cedar shingles then I would say use a metal roof. If your metal overlaps both pieces enough then you can get a pretty water tight seem just due to the overlap of the metal. Though taking it apart too much will bend the metal. I suppose if you attached all your shingles to plywood that hangs over in a similar fashion you might get the same result.


Homepage became white screen after successful data Migration with no error log

Question: Problem: White screen after data Migration.
Precondition:

I Migrate from Magento 1.9.1 to Magento 2.1.9 with lots of custom
extensions and customization. So I skip custom code & database tables migration .
I create custom theme and used lots of Magento 2 extension to
a fulfilled requirement like banners, testimonials, blogs.. etc

I successfully did data migration from Magento1.9.1 to 2.1.9. Links how I did Migration using Data-migration-tools (customers,reviews,orders,catalog,settings)
I tried both with settings and without settings. After successful migration, my home page became white with No error log
What I tried many times upgrade, compile code clear static content.
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento setup:static-content:deploy

I enable developer mode and set profiler also
bin/magento setup:mode:set developer

SetEnv MAGE_PROFILER "html"

when I see source code nothing wrong, means complete homepage code with inspect element/console.
How should I debug Now? any suggestion
Answer: I hope this will help you.
Try adding these lines to your index.php
Comment: It is bootstrap.php. Not index.php.
Comment: Sorry about the screenshot. It's index.php not bootstrap.php