Diagonalize mass matrix term for fermions and "doubling trick" in m(atrix) theory

Question: Can someone help me understand the "Doubling trick" at page 36 in http://inspirehep.net/record/887513/files/sis-2002-060.pdf (named "Scattering in Supersymmetric M(atrix) Models" by Robert Helling) or help me in some other way to get the mass for the fermions from the given Lagrangian, preferably without knowing the explicit form of the SO(9) gamma matrices?
Comment: Rather than link against the thesis, it would be better to put the trick/equation inlined here (with a reference to the text). Also, what is your confusion about it? Where it comes from, how to use it, why it works, etc?
Answer: Let $M$ be the mass matrix for fermions $\psi_+$ and for $\psi_-$ (separately). It is obtained by $\not{D}\not{D^+}= -\partial_t^2+ M^2$
Then $M^2=r^2 \mathbb{Id_{16}}- \not{v}$, Now, the $16*16$ matrix  $\not{v}$ has a zero trace, and it square is $\vec v^2 Id_{16}$, so the only possibility is that the matrix $\not{v}$ has 8 eigenvalues  $v$, and  8 eigenvalues $-v$ (here $v$ means $\sqrt{\vec v^2}$). So the matrix $M^2$ has 8 eigenvalues $r^2+v$ and 8 eigenvalues $r^2-v$. This is true for $\psi_+$ and for $\psi_-$, while $\psi_3$ is obviously massless.
[EDIT]
The gamma matrices of $SO(9)$ are real, so $\not{B}$ is hermitian. $\partial_t$ is antihermitian (because $i\partial_t$ is hermitian), so starting with $\not{D}=\partial_t-\not{B}$, it is easy to see that $\not{D}^{\dagger}=-\partial_t-\not{B}$
If you neglect order 3 terms in the Lagrangian ($\psi^2Y, \psi^2A$), and apply Lagrange equation on $\psi_+$, you get $\not{D}\psi_-=0$. And, because $\psi_+ = (\psi_-)^*$, and $\not{B}$ is real, you have also $\not{D}\psi_+=0$
The mass matrix apply separately to $\psi_+$ and $\psi_-$, simply because $\psi_+ = (\psi_-)^*$, and the mass matrix is real.
Comment: Why do we have a mass matrix for both $\psi_+$ and $\psi_-$ separately? And how come that if $\not{D}=\partial_t-\not{B}$ then $\not{D}^{\dagger}=-\partial_t-\not{B}$? And where do $\log$ come from? If it's from the effective action $\Gamma^{(1)}=\frac{1}{2}\text{Tr}\log (\mathscr{O})$ does that mean that $\not{D}$ is the wave operator for the fermions, and how do I see this?


Have not gone to parents grave in seven years

Question: A friend recently mentioned that she has not gone to her parents grave in over ten years due to its distance and when she wanted to go she was told by a Rabbi that if she has not been there for over seven years she has to send someone first to request forgiveness prior to going. What is the source for this? To which people does this apply? Why seven years?
Comment: That sounds like a superstition to me. Not that I'm any expert.
Comment: @SethJ: 1. Best one at the moment, but not really. 2. Yes, we don't. 3. I think so.
Comment: @msh210, is [tag:funeral-burial-levaya] really the right one here? Do we not have a cemetery or grave tag? Should we?
Answer: Nitei Gavriel Hilchos Aveilos 2 - 88:5 mentions that some people have a Minhag if they have not gone for 10 years to their parents grave not to go anymore. Then he goes on to say that there are those who after 7 years of not going to their parents grave do not go anymore. And he concludes that there are those who are not concerned about this at all. Sources mentioned are the Otzar Yad HaChaim 278 in the name of MaHarash M'Belz Zatzal, Mishmeres Shalom 5:32 and Mekor Chaim. It only applies to parents, and only if it was intentional. However if it was impossible to go then the deceased has no complaint and you may go. In 88:11 he mentions that by sending someone first to advise the deceased that the child is coming then even if the child was not there for 7/10 years the child may go.
Comment: I answered what I was able to find and the rest of the question remains. In addition there may be other answers.
Comment: Sorry to nitpick, but if you're going to answer your own question, I think you should provide a complete answer (or edit out part of the question.  You have not addressed why seven years.  On the other hand, if you want to edit the question so that you _include_ all of this information, you could then ask why seven years as the primary question.
Answer: The She'arim Metzuyanim BaHalachah (128:12) writes that the custom not to visit your father's grave after not seeing him for seven years has no basis in halachah, and we even have a proof to the opposite from the Zohar.
Comment: `after not seeing him for seven years` do you mean after not seeing his grave?
Answer: There are many different customs with regards to visiting graves.
The biography prefacing Igros Moshe volume 8 writes that Rabbi Moshe Feinstein didn't visit his father's grave -- "not the custom of Volozhin." Yet years later, when Rabbi Feinstein knew he would soon be leaving Eastern Europe for good, he traveled to his father's grave to say goodbye.


I'm missing my left leg, What can I do for exercise?

Question: I need help, like 4 months ago. I can't seem to get out this hole I'm in. I cant move around really well. I have gained so much weight. I need advice.
Comment: Where are you at in terms of rehab? I think that's generally the first step in regaining mobility after amputation. If you have a prosthetic, but coordination is your main limitation, you could try a rowing machine and just keep your legs straight. (Generally, I think you're supposed to use your legs on rowing machines, but upper back only would be better than no exercise at all, I guess.
Comment: It may help users attempting to answer this question if they knew a bit about what you've been trying and what hasn't worked and even how you're feeling about it (a psychological answer could potentially be found in another SE)
Comment: Take a look at the Men's Health from a month or two ago. Their man of the year has one arm and one leg and is in amazing shape. (Combat veteran).
Answer: These days you can do just about anything you want.  Adaptive equipment is available for most activities and sports.  Prosthetics have come a long way and your rehab team and prosthetist should be able to help you meet your goals.  The "blade runner" ran in the Olympics.
When you think about it, everything we use is some type of adaptive equipment.  A car is designed to adapt to our bodies with the steering wheel for our hands and the pedals for our feet because that is how most of our bodies are arranged.  But if you don't have use of your legs, these days you can have all the controls at your hands.
The same goes for exercise and sports.  If you don't have a conventional body, someone has a non-conventional adaptation to help you achieve what you want to do.  Start with whatever it was that you liked to do before and have your rehab team get to work with you.  Best of luck.
Answer: Go talk to your physio, as they'll be able to give you some tailored suggestions, in addition to the usual balance / flexibility exercises. Anyway a few ideas you could discuss with them:

Making it from one side of a hospital to the other. For places built for the sick and infirm most are very poorly designed, and a bit of an obstacle course, especially if in a chair or on crutches. So best to think of them as specifically designed obstacle course, intended to help patients regain condition, otherwise the frustration and the physical effort required to navigate their corridors may leave you in a tachycardic state. The number of magnetically locked fire doors that require you to press a wall mounted release button with one hand and pull the door open with another is amazing, till you realise they're only there to build and test your balance, coordination and upper body strength.
Swimming, back stroke, assuming you can find a pool with suitable access, and initially some suitably trained life guards to natter to. They'll lose interest in you once you can do 1000m. Just make sure the pool has a very shallow end, or a lift, else getting out may be interesting, and amuse any kids in the vicinity.
Walking, if only a few hundred yards a day to a post box or shop. Initially even this may leave you a sweating wreck.
Modified Push ups / Planking, if only a few, as good for the back as well as the upper body.
Sit ups, but be careful, you'll have lost a lot of conditioning, and your glutes will more than likely be rather flabby, so only a few or you'll end up with carpet burns.
Pilates / Yoga, to stretch muscles you never knew you had.

On the weight front, start to keep a food diary, or probably easier to use an App such as MyFitnessPal. It should help you work out where the majority of your calories are coming from, and where you can cut down. Note as your activity levels will have probably been reduced to the Sedentary classification, so your daily calorie requirement may be a third lower than that of an active individual.


High School Geometry Text?

Question: This year I will be teaching 8 hard-working home-educated teens a Geometry course.   Back in 1994-1999 I worked full time as a High School educator, taking a turn teaching everything from Pre Algebra through Basic Calculus, and Geometry was (and still is) my favorite.   I am wanting to buy (at abebooks or some such place) a stack of student books and a teacher's edition.  Recommendations?    In some ways the recent editions may be better.   In other ways . . .  not so much.  I recall being aghast as a teacher at how "dumbed down" the texts had become just in the few years between my being a high school student and a high school teacher.  And that was 20 years ago.  If you have a specific publisher and year (Prentice Hall 1989, as a random example) that you enjoyed using as a teacher, I'd love to hear your comments.
Comment: Try http://matheducators.stackexchange.com.
Comment: I don't know have any textbooks to recommend, but I was curious whether something interesting would turn up if I poked around what's used in some high school honors geometry courses (unfortunately, in the past 20 or 25 years I think "honors" has come to mean little more than what "college prep" meant 40 years ago), and I found [this interesting page of parent comments](https://www.berkeleyparentsnetwork.org/recommend/schools/BHS/honorsgeom). Anyway, for starters try googling "honors geometry" along with "high school".
Comment: I recently read somewhere (forgot where, but it wasn't on the internet) about the existence of a high school geometry book co-authored by [George David Birkhoff](https://en.wikipedia.org/wiki/George_David_Birkhoff). I haven't seen a copy of the book yet, but any serious attempt by someone as renowned as G. D. Birkhoff is very definitely worth looking into. See [**Basic Geometry**](http://www.amazon.com/dp/0821821016) (3rd edition) and [**Basic Geometry - Manual for Teachers**](http://www.amazon.com/dp/0821826921), both by George David Birkhoff and Ralph Beatley.
Comment: I'd recommend [advanced high-school mathematics by David B. Surowski](https://www.math.ksu.edu/~dbski/writings/further.pdf).
Answer: How about Lines and Curves by Gutenmacher and Vasilyev (Springer, 2013); about this book:

"Lines and Curves" is a unique adventure in the world of geometry. Originally written in Russian and used in the Gelfand Correspondence School, this work has since become a classic: unlike standard textbooks that use the subject primarily to introduce axiomatic reasoning through formal geometric proofs, "Lines and Curves" maintains mathematical rigor, but also strikes a balance between creative storytelling and surprising examples of geometric properties.

I didn't finish reading the book, but as to the parts I have read, I can attest to the summary. Here is the book at AbeBooks.
Answer: If you don't have any particular curriculum to follow, the best textbooks in English are probably the ones commonly used in England during the period 1910-1960 approximately.
The most frequently recommended school books in bibliographies seem to be those by C.V. Durell and by H.G. Forder.

A number of Durell's textbooks can be found here. A New Geometry for Schools is for beginners. Modern Geometry is more advanced.
Forder wrote A School Geometry and Higher Course Geometry. I only know the latter book, which is more advanced, but I believe they're both aimed at high-achieving students.

Kiselev's Geometry was recently translated from Russian under the titles Planimetry and Stereometry. I think the textbook is relatively good, but unfortunately, the translation is poor, as it was done by a non-native speaker of English.
In French, I would recommend the series by Hémery and Lebossé. In Russian, the books by Pogorelov are good, as well as the ones by Aleksandrov, Verner and Ryzhik (for students in so-called "mathematical schools").

High School Geometry Text?


How can I get the Skype notification back in the system tray?

Question: I am running 11.04. I have Skype running but it does not show up in the notification tray. It was working until I added Skype to auto-start when I log in. Does anyone know how to make it reappear?
Comment: One other option you might consider is adding Skype to the messaging menu:  http://www.omgubuntu.co.uk/2011/04/how-to-add-and-control-skype-via-the-ubuntu-messaging-menu/
Answer: You can get skype tray in 11.10 and 12.04 installing package sni-qt:i386
sudo apt-get install sni-qt:i386
OR
You can whitelist systray as well
How do I access and enable more icons to be in the system tray?
OR
If you like how empathy and messaging tray work you can install a third party skype-wrapper package from ppa which enables Skype to indicator-message

You can install it with
sudo add-apt-repository ppa:skype-wrapper/ppa
sudo apt-get update && sudo apt-get install skype-wrapper

SOURCE
Comment: cool, whitelisting the systray to 'all' worked! thanks
Comment: sni-qt:i386 installation on 64bit machine solves the skype tray problem in ubuntu 12.04 too (gnome classic with no effects)
Comment: skype-wrapper is indeed a very nice thing to have. A shame that it's still a bit buggy.
Comment: is there an update for Ubuntu 14.04?
Answer: Install dconf-tools  / sudo apt-get install dconf-tools.
Then run the conf editor by typing:
dconf-editor

at the command line.
There under Desktop > Unity > Panel

change the line that says:
['JavaEmbeddedFrame', 'Mumble', 'Wine', 'hp-systray', 'scp-dbus-service']`

into this here:
['JavaEmbeddedFrame', 'Mumble', 'Wine', 'hp-systray', 'scp-dbus-service', 'Skype']

You can change it to ['all'] which allows all tray applications to show there icons in the indicator bar (Ah-Duh!). As usual changes will take effect only after reboot or restarting unity by Alt+F2ing
unity --replace &

Answer: Make sure you are not experiencing this bug (Launchpad.net)
Sometimes, the Skype indicator is only one green pixel. It's easy to overlook and assume there is no indicator at all.
If this is the case, just quit and restart Skype and it will come back normally. I have this quite often.
Comment: Thanks JE2Tom. I am experience the green pixel in the notification area. But i fail to get a proper icon even after restarting skype. It come up again just as a pixel.
Answer: I have figured out the cause and the fix, at least in my case.
The problem was that Skype was loading before the systray application.  The solution was to delay Skype on start up.  Someone else may have a more programmer worthy fix, but my solution was to change my KDE startup options to "start with a blank session" instead of remembering the last session.  I then created a file in ~/.kde/Autostart with the name skype.sh. Here's the text I put in mine:
#!/bin/dash

sleep 15
/usr/bin/skype
exit

Afterwards I did chmod +x ~/.kde/Autostart/skype.sh
It's working great.
Answer: For me in 14.04;

Open dconf-editor
Search systray (couldn't find in other answers on mine)
On show-icon-on-systray click off the tick then back on again, then click restore default button.


Why can a red laser beam reflect in a blue surface?

Question: I've been taught that a blue object only reflects the blue fraction of light, and all the other colors are absorbed. So what happens with a red laser?
Answer: Your teacher was oversimplifying.
A surface looks blue because it reflects more light in the blue portions of the spectrum than in other portions.
But less is not none. It's very rare for a surface to be completely non-reflective.
Your laser pointer is much brighter than the ambient light. So even if most of the light is absorbed you still get enough reflected to produce a red dot.
Comment: How many intensity does the ambient light have? Let's suppose it's X. If I had a laser pointer with X intensity, then in a dark room I point it at a blue surface, I won't see nothing?


My VDB from embergen is blocky and pixelated

Question: apparently I have exported my vdb from embergen, and I have imported them to blender, they seem to be too blocky and pixelated, I have spent hours on trying to find a fix but no sauce. Any help will be appreciated!
Answer: Try increasing the samples and/or decreasing the tile size in the Volumetrics Settings in the Render Properties tab. Start and end work to increase resolution as well, however these settings modify the volume visibility based on camera distance, so be careful that your camera will remain within the distance range:
Comment: Well, that did improve it but just by abit.. it still looks very blurry and the animation looks so wonky, not same at all comparing to Embergen. I have added a new pic


How to create shape keys from posing armature?

Question: I have one character with his face rigged and I want create shape keys from posing bones of his face, I'm trying to do this with the armature modifier but when I make clic in Apply as shape key, this create the shape key but my armature unlink of my mesh, so I copied the modifier before apply as shape key, but the pose doesnt back to original pose. Is there another method to do this or what I'm doing wrong?
Answer:
Set the pose you want
In the armature modifier save as shape key (previous versions of Blender require apply followed by recreation of the modifier).
Go to the object data tab and rename the new shape key (it will be named after your armature).

In this way you will have the mesh controlled by the armature and a shape key which will reflect the pose you set in point 1)
Comment: @Ben Jackson Formatting is a fine edit, but I think your answer is significantly different from the one here and deserves to be its own answer to the question, and so I have to reject your edit.


What would be my affiliation if I'm a Masters student?

Question: The question title pretty much says it all. I'm now a graduate student pursuing my Masters degree. Will the university I'm enrolled in be my affiliation when writing a paper?
Comment: Well, what else would it be?
Comment: @Eppicurt - Thanks. This is my first time writing a paper, so I'm just making sure. Have a good day :)
Comment: I've seen several math papers in recent years (in MAA journals) in which one or more of the authors is a high school student, and their high schools are listed for their affiliation, and I thought nothing of it besides being impressed.
Answer: Yes.
And be sure to get it in there before you graduate. Though if you are not moving straight to another uni and plan on publishing more, if you talk to your prof they might hook you up with "affiliate" status. This means no money or much of anything else other than the ability to claim affiliation.
Comment: At least from my experience it is pretty common to use the affiliation at the time the research was conducted and not necessarely the one at the time the manuscript was submitted.


JavaScript A/B testing with Google Analytics

Question: I want to start A/B testing on some pages on my site. I will change some elements (buttons, text, images, etc.) by JavaScript code - so I don't want to create duplicates of every pages with changes. It is clear, but next I have a problem with measuring this tests - how I can see in Google Analytics which users have a one variant of test and which see another? I want to see all next actions of this users. Should I use custom variables in GA?
I know, that, for example, https://www.optimizely.com/ can do all this things, but I just want to know how I can develop this by myself.
Answer: It sounds like what you want is a Google Analytics feature called Content Experiments.
This article explains how to set this up on the client side using JavaScript:
https://developers.google.com/analytics/solutions/experiments-client-side


Export layer as a file in Adobe Fireworks

Question: I'm trying to export a layer in fireworks to an image file. When I go to file>export and select layer, it exports everything to one file (no different from saving a fireworks image).
How do I accomplish this easily?
What I'm doing now is create a new image, copy the layer and save it.
Answer: File → Export…
Choose Layers to Files from the dropdown. Under the Options… you can choose the target file type (or you can choose to use the document's optimization settings set in the Optimize window).
Then Fireworks exports the layers (all visible) as separate files. (If you want just one layer, you can hide the others.)
Also note that Fireworks' layers are represented as folders in the Layers window, unlike in f.ex. Photoshop.
Comment: what if I want to export all of my bitmap "layers", not "folders"? Can I convert a "bitmap" to a "folder layer"?
Answer: If I understand the need - this extension does the magic:
http://johndunning.com/fireworks/about/ExportSelection
You select the object(s), or layer(s), and choose Commands > Export > Export Selection - Background Transparent. There are more options, but this is the common and best one. It will export a SINGLE image with the layers you picked on alpha transparency.


Creating Leaflet layer that can be toggled in layer control from CartoDB viz.json?

Question: How do I create a leaflet layer that can be toggled in the layer control from a cartodb viz.json? I have read that the cartodb.createlayer does not create a leaflet layer. It seems you can add the cartodb table, but of course that takes away the whole point of using cartodb for easy visualization. This seems like a basic function, I am a novice in terms of coding so maybe I am missing something.
Comment: please break this up into 3 separate questions
Comment: http://jsfiddle.net/q5uy3bh2/2/
Comment: one hack I did was to change the opacity of the tile layer, revealing the cartodb layer but keeping layer control available
Answer: Putting the layer control inside the cartodb callback like this seems to work, but the legend remains. Also not sure how this would apply to multiple cartodb layers, but this essentially answers my question. Setting the index value is key to getting the cartodb layer to draw above the tile layer without losing the leaflet layer control:

<code> var cdb_url = 'http://ovrdc.cartodb.com/api/v2/viz/52a89830-a8c1-11e4-b072->0e0c41326911/viz.json';
 cartodb.createLayer(map, cdb_url)
   .addTo(map)
   .on('done', function(crashes) {
        crashes.setZIndex(2);
        var overlayMaps = {
          "Vehicle Crashes": crashes
        };
        L.control.layers(baseMaps, overlayMaps).addTo(map);
   })
   .on('error', function(err) {
     alert("some error occurred: " + err);
   });
</code>


Can I run Android Nougat?

Question: So I just ordered a new phone (Honor 5x) I need to know can I install an early version of Nougat & when its released will it operate on my phone? Thanks!
Comment: Please see: [When will my device get the Android 7.0 update (Nougat)?](http://android.stackexchange.com/q/139232/16575) (which is our generic page for this question) If your device isn't listed there yet, we probably have not yet obtained data on it. If it's not released for your device officially, there might be some custom ROM for it one day; but such things are better checked at XDA, where most of the custom ROM creators are active.
Answer: Unless you have a Nexus phone currently, you cannot run it.  When it is released, the manufacturer of your device will release it so I assume it will then operate on your phone.

Can I run Android Nougat?


can i use java code as it is in a jsp file?

Question: Please forgive me if my question sounds too dumb :(... I have created a java desktop application, which has a single UI screen in Swing... The application creates a pdf report... I want to convert this application into a jsp based web application. So do I just have to create a simple screen where the parameters required to create the report are asked, this screen replaces the swing based UI... and the main  block of java code (used to create the report with the help of input parameters) can be invoked from a jsp file? Is that it? Or is something more significant required to make this app into a web app. How do I find out what else is required?
Answer: You should have a web server. Create a web archive (.war) from your code base by reusing Java classes and new jsp file (UI). So your understanding is correct. and remember there won't be any main method now.
Answer: Yes - JavaSE code is the same Java on server side. You have to change UI. You may use plain HTML or web framework such as JSF.
Comment: Quote: "So do I just have to create a simple screen where the parameters required to create the report are asked, this screen replaces the swing based UI"
Answer: This highly depends on your code. Business logic and PDF generation might be reused but the UI will definitely be replaced. You'd then also have to account for the download part, i.e. the response could be a page with the DL link or the generated PDF.
Edit: as Azodious already stated, you'd need a webserver like Tomcat (or JBoss which is a fully fledged application server and includes Tomcat) that is able to execute the Javacode, so just replacing the UI wouldn't help much.


Protect opera user profile

Question: Is it possible to protect or encrypt complete opera user file including bookmarks, history, settings etc. so, that a different profile can be used whenever needed? I wonder if there's a built in or third party plug-in would allow to do that. I would also like to know the manual way if there's one for Opera 11.
Answer: I don't see how encryption or write(?) protection could help to use multiple profiles in Opera, but since this is what you probably want: Yes, it is possible.
For the current version on Winows this requires renaming of a existing profile directory, some INI editing (fixing paths) in your opera6.ini and running opera.exe /settings "path\to\your\opera6.ini", as described in detail on http://operawiki.info/operaprofiles.
For the upcoming Opera 12 it is easier: just run opera.exe -pd "path\to\opera\profile" - Reference is here: http://my.opera.com/ruario/blog/2011/09/28/the-pd-personal-directory-switch
Answer: No, you have to encrypt your different profiles manually. For which if you want to do in the same Windows account you will need something like TrueCrypt.

Protect opera user profile


Resource Planning Question

Question: Does anyone know how to plan one resource in Project 2010 when the touch time for that resource for the task such as reviewing something is only 5 hours, but I am obligated to have the object in a review cycle for 5 days?  Review cycles may have multiple reviewers and will never total the 5 days.
Answer: Separate out the effort (work) from the cycle time (duration). In the Gantt chart view you can add separate columns for those, and enter 5h for work and 5d for duration.
The scheduling engine calculates based on work and % allocation of the resource. If the resource is allocated at 100% or 1 FTE on that task, the scheduler will front-load the 5h on the first day of the review cycle. If you want to change that, go to the Resource Usage view, double-click on the assignment (italicized task name), and change the Units (% allocation) and Work Contour until you get the result you're looking for.
When I'm leveling a resource in this way I use the Resource Allocation view, which shows the Resource Usage on the top half of the screen and the Levelling Gantt on the bottom. Remember that the line items in italics on any Usage view are assignment objects, not tasks or resources, and they have their own attributes; so changes to duration & dates of assignments may not carry through to the task item.

Resource Planning Question


Can I have extra minecraft inventory?

Question: Can I have extra Minecraft inventory in vanilla Minecraft?  I have seen mods be able to do this but never in vanilla Minecraft.  Is there some way for me to carry more.  Maybe  a command that allows me to carry more than a stack of 64 or have more slots to carry more.  I cannot figure this out, if there even is away.
Comment: Are you surviving or what?
Answer: There is no way in vanilla Minecraft to expand your inventory, whether by commands or by other means.
If you wish to have a larger inventory, you could try making an Ender Chest and using one slot of your inventory to carry it around. Note that you need a silk touch pick in order to pick it back up.
This would mean you can have up to 61 inventory slots (63 minus two slots to carry the Ender Chest and pick) and 4 armour slots total. This is 25 more than the normal 36 slots.
Comment: To use the Ender Chest as a backpack of sorts, you will need a Pickaxe with Silk Touch. This requirement removes one more slot, or you'd have to carry multiple Ender Chests which may be become pretty expensive.
Comment: You could also take a mule.
Comment: You should put in shulker boxes as well. You can break shulker boxes and they will keep their items.
Comment: @Thorsal Good point. I have edited my answer to contain this info.
Comment: Ore take a stack of eyes of ender. But who's got time for that...
Answer: Shulker Boxes deserve a dedicated answer of their own.

It is now possible to have extra inventory slots (as of 1.11).
You simply need a Shulker Box...

27 item slots
can be placed and broken
they keep their inventory when broken, so you can access it after placing the box again
can be placed in your inventory and other containers
cannot be placed in other Shulker Boxes
unlike chests the Shulker Box will be facing away from the block it's placed against
you can give it a name using an Anvil.
Comment: For anyone playing Survival, Shulker Boxes are a very end-game item (one of the last items in the game you'll be able to craft), so for the vast majority of a survival game for most players they are unattainable.  If you are playing creative mode you don't need inventory as you can just spawn whatever you want whenever you want.
Answer: I don't think that there is a way to have more room in your own inventory.
Instead, there are other ways to carry more:

Build a "donkey train". Attach chests to some donkeys (or mules), mount one of them, then use a lead to pull the others with you. With this method, you can significantly increase your storage slots, with 15 per donkey.
Use Ender Chests. They act like "cloud storage", meaning that the items you put in one, can also be picked up from another one that's far, far away. Furthermore, what you store in them is private, giving you a world-wide storage available only for you, increasing your storage slots by 27.
Use Shulker Boxes. They condense a whole chest's worth of storage into one block that cannot be stacked, but can be placed down and picked back up with any tool without dropping their contents.
Carry your items in "packed" states, like:

Blocks of ore instead of materials (ores)
Bones instead of bone meal
Logs instead of planks
Etc.

This method may help you to preserve your already existing slots. Sometimes it may help you to make massive slot savings, or sometimes it may be insignificant.
Answer: Fill your inventory with shulker boxes full of 64 stack items, then, in your off-hand, hold an ender chest full of 27 shulker boxes with 27 stacks of 64 stack items, and wear armor for max item storage.
Comment: Welcome to Arqade! Please take the [tour](https://gaming.stackexchange.com/tour) and visit the [help center](https://gaming.stackexchange.com/help) to learn how things work around here. Your solutions has already been provided in the other answers, so if you have a new solution that has not already been covered, you can include it to improve your answer.
Answer: I dont think there is a way to increase your OWN Inv, but ender chests and shulker boxes would be a way to have more storage
Comment: Hi! Both options have already been suggested in the existing answers. Please don't duplicate information. I suggest taking the [Tour]. Welcome to Arqade!

Can I have extra minecraft inventory?


Kinetic energy and temperature

Question: I've randomly been thinking about smoothies and internal energy all weekend. If we have an assortment of fruit in the solid phase and then proceed to blend it all so that it ends up being in the liquid phase, am I right in saying that work has been done on the solid fruit such that its internal energy is higher, therefore it remains in the liquid phase at the same temperature as the room (once thermal equilibrium is reached). I'm having a bit of difficulty in understanding how another identical assortment of solid fruit and the smoothie liquid can both be at equilibrium if their kinetic energies are different (liquid has more than a solid right?). I thought that kinetic energy determines temperature??
Answer: Well, is fruit really in a solid phase? Consider that fruit consists of a lot of water; that water is in a liquid phase prior to blending. Saying that fruit is a solid is like saying a water balloon is solid.
When you blend the fruit, all you're really doing is slicing it up. What's left is fragments of fibres, membranes and so on in a liquid-ish suspension because you also freed up water in the process.
Of course the blending itself adds some energy but this is negligible.
To answer your question on a single line: There's no difference in molecular kinetic energies or temperatures because there are no phase transitions on a molecular level.
Comment: Thank you for that. Yes that makes sense to me now. What about a glass of water and water vapour together at thermal equilibrium in a room? The vapour has more kinetic energy right? Yet they are the same temperature. Wouldn't there also be more potential energy in the vapour? So more total energy as a whole and yet it is at the same temperature?
Comment: Water vapour as in fog or clouds is just a bunch of microscopic water droplets. In  a true gas phase, evaporating requires a certain amount of energy, you could think of it as the gas 'holding' potential energy.

Kinetic energy and temperature


Fitting model to data

Question: I have been trying to adapt some of the previous suggestions on other questions similar to my problem but I haven´t been able to solve my problem so far.
Best wishes
Comment: The question as it is, gives no clues about what to do!
Comment: Yes, I would like to delete the question. It could not get solved and other threads are very similar and have very detailed and excellent solutions to similar problems. For this particular question the solution was not working. Therefore I would ask to delete the whole thread, please
Answer: It looks like this question can be answered following the answers in this discussion: "Multi-peak fitting for peak position".
I was too lazy to figure out a basis with the functions you want to fit. (You have listed many parameters.) So, I used the Gaussian function in this answer:
gaussian[amp_, pos_, fwhm_, x_] := 2^(-((4 (-pos + x)^2)/fwhm^2)) amp

Here are the obtained fits:

If you can come up with a reasonable basis using code similar to this one:
aBFuncs =
  Association[
   Flatten@Table[
     pos -> gaussian[amp, pos, fwhm, x], {amp, {1}}, {pos, Min[data[[All, 1]]], Max[data[[All, 1]]], 0.05}, {fwhm, {0.3, 0.1}}]];

then you should be able to get the fits you want.
Comment: Thank you very much for your help! The data is going from top to bottom, so the peaks are not upwards but going from the top downwards.
Comment: @FredWeker "The data is going from top to bottom, so the peaks are not upwards but going from the top downwards." -- It should not matter if the function basis is chosen right.

Fitting model to data


Greeks across different underlying

Question: To monitor risk of a client portfolio, does it make sense to accumulate Greeks across different underlying? If yes, how can Greeks be normalized across different underlying?
Answer: It depends on what kind of 'Greek' and 'underlying' you are referring to.
Aggregating the sensivity of various equity positions (e.g. options, futures) to interest rates could for instance make sense if you want to evaluate the sensitivity to that common risk factor.
On the other hand, aggregation of underlying-dependent quantities (such as Delta) across distinct underlyings, does not make sense, at least in the equity world.
That being said, aggregation across a different positions/instruments written on a given underlying asset does of course make sense (e.g. macro hedging of the Delta, or bucketed Vegas).
Comment: I am particularly interested in aggregating Delta and Gamma.
Comment: For a given underlying across a portfolio? Or really across different underlyings as you claim? What kind of underlying: equities, fx, interest rates, commodities?
Comment: We have been aggregating for a given underlying across a portfolio. I wanted to know if we can aggregate across different underlyings , to be more specific futures and option positions with underlying as equity indices and various equity stocks.

Greeks across different underlying


Doubt regarding a question DS160 application (countries you have visited)

Question: While filling DS160 I bumped into this question which was asking about the  countries I visited. Should I mention transit too? Because I had a transit in Germany (when travelling from Sweden to India) and in Denmark (while travelling from India to Sweden) in the years 2020 and 2019 respectively. I have the stamps in my passport too. Do I have to mention in the form under the question of visited countries? I'm really confused? I tried finding the answer but I couldn't find any relevant to transit. Could someone please guide me with this?
Answer: If you have the stamp on your passport, include it as a visited country. If they ask the reason, just mention you were in a connection
Comment: Good answer.  I would go farther and mention transit countries even if there was no stamp (for example, Germany in transit from the UK to India).  In general, if you're unsure about whether to mention something, mention it and let the authorities decide whether it's significant.  They're far more likely to react unfavorably if you fail to mention something they want to know about than if you do mention something they don't care about.  On my US customs declarations I write _(transit),_ but I don't know whether this is possible with the DS-160.


Long Layover in Korea

Question: I am a Philippine passport holder and I have a 14 hour layover in Korea on January 29. My problem is that my passport is expiring on April 21. When I called Asiana before I booked my flight, they said that boarding wont be a problem since my final destination is the Philippines and I am not going out of the airport in Korea. However, some people are telling me that Asiana might not board me on the plane because of my passport. Can someone please assure me that I won't have that problem and that I will board smoothly.
Comment: For completeness, what is the point of origin of your journey?
Comment: flying from lax - inc then inc - mnl
Comment: Do you mean ICN? INC is way up in northern China.
Comment: yes. sorry. i meant ICN
Answer: Your friends are probably referring to the so-called "six month" rule where some countries require a passport to be valid for six months before accepting it.
The six month rule does not apply to your proposed itinerary. Both Korea and the Philippines accept Philippine passports up to the day of expiry.

Long Layover in Korea


Arya Samaj Translation of Vedas

Question: I was looking at Arya Samaj's translation of Vedas on onlineved.com and found that the Rig Veda is missing Mandala 7-10. Why is that? Also the way they cite the verses is quite different than the traditional method.
Comment: Dayananda Sarasvati died before completing the translation of Mandal 7-10.
Answer: It's available as book. You can read this online. They mentioned Mandala, Sukta on the above of the page
https://elibrary.thearyasamaj.org/book/rig-veda--volume-iii
Answer: https://archive.org/details/wg868/mode/2up
Here you can find whole rig veda of translated by arya samaj. Arya samaj believes that vedas is scientific document and doesn't have any geography or history .example in nadi suktam , arya samaj claims they are not rivers rather they are arteries. That's why their commentary is different from traditional though they claim their commentary is based on yaska and dayanand saraswati

Arya Samaj Translation of Vedas


Another Term for "Long-Thought"

Question: So I was doing a bit of writing and ended up using the phrase "long-thought" (as in, "a technique long-thought forgotten" or "people long-thought incapable of using magic"). I ended up using it quite a few times and was wondering if anyone can come up with another phrase with the same (or a very similar) meaning so that I won't constantly be using the same word. Thanks to anyone who can help!
Answer: Synonyms to the rescue. The term is Believed to be. The Coelacanth was believed to be extinct until one showed up off the coast of Madagascar.
Answer: Received knowledge was that Trump was not a serious candidate.
I learned this phrase from listening to BBC news programs.  It means what was popularly believed.
You can also use that: popularly believed.  For example:

At one time, it was popularly believed that Mars was criss-crossed with canals.

The common or popular conception was that etc.
You can also try

people previously thought [to be] incapable of using magic

In other words, leave out "long."  (This "to be" is optional.)

Another Term for "Long-Thought"


Configure mounting timeout at boot

Question: On remotely rebooting a 12.04 machine I found it hanging at the "unable to mount soandso: Skip, Manual Abort? " (That's pretty much how I remember the message) The machine was basically stopped there until I hooked up a keyboard and pressed "s". I can see the rationale for the question, but I'd really like to know where to configure it or turn it off altogether. A mandatory question like this makes sense in a desktop environment but for servers I'd like more flexibility.
So where do I fiddle and tweak this?
Comment: check your settings in /etc/fstab
Comment: may this helps http://unix.stackexchange.com/questions/29196/automount-nfs-autofs-timeout-settings-for-unreliable-servers-how-to-avoid-han
Answer: Now it is 2020 and this question can be updated to represent current status. In a nutshell, the timeout can be set by using x-systemd.mount-timeout parameter:
From manpages:

Mount units may either be configured via unit files, or via /etc/fstab (see fstab(5) for
details). Mounts listed in /etc/fstab will be converted into native units dynamically at
boot and when the configuration of the system manager is reloaded. In general, configuring
mount points through /etc/fstab is the preferred approach.

and:

x-systemd.mount-timeout=
Configure how long systemd should wait for the mount command to finish before giving
up on an entry from /etc/fstab. Specify a time in seconds or explicitly append a unit
such as "s", "min", "h", "ms".

Thus, for example:
/dev/sdc     /mnt/backupdir     ext4     defaults,x-systemd.mount-timeout=30 0 2

waits atmost for 30 seconds during the boot for that entry to be mount before give up.
Answer: Thanks for the hint with the console message; it saved me having to plug-in a monitor to the console of a test server (keyboard sufficed...)
That said, up to at least 14.04, Ubuntu supported a nobootwait option for fstab entries, which would achieve what you want; smth like this:
UUID=8b481900-fb7a-4e9e-929c-e940a6b913a4 /data   ext4   nobootwait  0  2

Alas as mentioned in this other question, the nobootwait option was removed in 16.04 with currently no viable substitute other than the /etc/rc.local workaround described in the other answer.
Answer: Remove the mount by editing or commenting it out in /etc/fstab and replace it with an explicit mount command in /etc/rc.local.

Configure mounting timeout at boot


Use repository name in travis CI

Question: I am facing an issue on Travis CI. I seem not to be able to use the repository name as an environment variable.
I have a Travis build that is setup to build, tag and push a Docker image.
In the after_success section of the .travis.yml file the following command is running
docker build -t ${PROJECT}:${TRAVIS_BRANCH} .

(The environment variable ${PROJECT} is the actual name of the repository and is set in the repository settings.)
The problem is that Docker is using "[secure]" as image name instead of the repository name. I end up with something like
Successfully tagged [secure]:staging

After that when I am tagging the image the following error is returned
Error parsing reference: "/[secure]:staging" is not a valid repository/tag: invalid reference format

I have tried to update ${PROJECT} to a random string and it worked fine.
Is there a way to use the repository name as a environment variable?
Answer: It seems as if your $PROJECT contains a leading slash which might be the problem.

Use repository name in travis CI


Using the Datumbox Machine Learning Framework for website classification - guidelines?

Question: A short while ago, I came across this ML framework that has implemented several different algorithms ready for use. The site also provides a handy API that you can access with an API key.
I have need of the framework to solve a website classification problem where I basically need to categorize several thousand websites based on their HTML content. As I don't want to be bound to their existing API, I wanted to use the framework to implement my own.
However, besides some introductory-level data mining courses and associated reading, I know very little as to what exactly I would need to use. Specifically, I'm at a loss as to what exactly I need to do to train the classifier and then model the data.
The framework already includes some classification algorithms like NaiveBayes, which I know is well suited to the task of text classification, but I'm not exactly sure how to apply it to the problem.
Can anyone give me a rough guidelines as to what exactly I would need to do to accomplish this task?
Answer: You can make use of the text classification class for your task.first make sure how you are going to classify the websites.(i.e as sports site,health and wealth site etc).Get some training data and train them & Done


Op-Amp working principle

Question: In the op-amp working principle I was told that if I have a certain input voltage at the non inverting pin, then the inverting pin will also be forced to have that voltage and hence if I attach a feedback impedance to the output, then the output voltage will align itself in such a way that KVL and KCL are conserved along with reflection of a followed voltage at the  inverting pin. My question is, why does this reflection of similar voltage at the inverting pin happen depending on the non-inverting pin? Can I also reverse the ideology? That is if I were to have a voltage V0 at the inverting pin and attach a feedback at the non-inverting pin, will it follow the voltage at the inverting pin?
Answer: What you were told is not theoretically correct. You have to change the way o thinking what really happens. It is the feedback loop that can force IN-=IN+ , not IN-=IN+ that makes the loop work.
The condition IN-=IN+ des not happen magically.
Start thinking that \$Vout=A_0(IN_+-IN_-)\$ where \$A_0=10^6\$
This is the IN\Out relation of an open circuit (not in a feedback loop) OPAMP
When you close the OPAMP in a negative feedback loop with resistance \$R_1,R_2 \$ this relation is still valid but the loop will change everithing
When you apply a voltage to the IN+ of the OPAMP, at time \$T=0^+\$ its output will  saturate to \$V^+\$(positive rail) as \$IN_+=Vin\$, \$IN_-=0\$ and so \$Vout=10^6(Vin-0)=too much\$.
Then, thanks to the feedback loop \$IN_-\$ will go from \$0\$ to \$V_{out}*\frac{R1}{R_1+R_2}=V^+*\frac{R1}{R_1+R_2}\$.
What happen next is that the value of \$V_{out}\$ will change as the value of \$(IN_+-IN_-)\$ chaged thanks to the loop. As a conseguange the value of \$IN_- \$ will change again and again Vout and \$IN_-\$ again and so on.....
At this point you should understand were we are going, as we have a negative feedback Vout and \$IN_-\$ will change until you reach a point of equilibrium. The point of equilibrium is when you have \$IN_-=IN+\$
This ideology can be reversed but be carful that in the other case the loop becomes a positive one and instead of reducing to  \$0\$ the difference \$IN_--IN+\$ this will increase untill you reach another equilibrium point that is in this case \$ V_{out}=V^+\$
Answer: No, reversing the idea results in positive feedback, instead of the negative feedback that's required for the principle you're talking about to hold.

Op-Amp working principle


How to place 3 textbox in 1140px width of card? There are 2 tabs in card. width is fixed due to content in other tab

Question: The width is 1140px width.
The content in tab 1 is more and takes width 1140px.
so to maintain consistency can't change or make smaller width
Suggest any other layout or better solution
Find attached wireframes
Comment: I don't see a problem with your design. I agree, keep the tab sections the same size. even if that results in great expanses of white space. Also you have the button near the fields. Bravo.
Answer: You could rearrange textbox 1,2 and 3 in columns. Also consider that fixed widths are almost inexistent right know so you should design the columns with proper responsive behavior.
Comment: Sorry I forgot to mention about it but the Tab is "Change Password".
So It have 3 Textfield's as 1. Old password 2.New Password 3. Confirm Password.
And I think it is not good UX to put these fields in columns
Comment: Ohh it's a form, that change everything, in this case textfields should not be in columns, I think the whole component should not use the full width, it could be centered on the viewport or parent element.
Comment: Centering will break the consistency. The form in tab 1 is left aligned. It cannot be center aligned because of large no. of textfields.
Check this wireframe https://i.stack.imgur.com/6Vogl.jpg
Answer: If you are in need of using the same card for both tabs (wide and short) your options are:

Reduce the widest tab
Keep empty space in the shortest tab

As you mention that Option 1 is not possible then you can only keep the long width in the short tab.
Empty space is not a problem in your design. So you can just keep it. The only thing is the action button (reset password) should be either on the right or on the left of the tab.
Comment: The container I have used for whole project is 1140px. So I have to maintain this card in this width. Also The "Tab 1" is having large number of textfields where as tab 2 which is "Change Password" is having only 3 fields. Have a look at this wireframe. https://i.stack.imgur.com/6Vogl.jpg
Comment: The answer was according to that image. I don't find there is much problem with the empty space. It looks good to me.
Comment: Okay. Have a look at the first tab content and then 2nd. - -
1st tab http://i.imgur.com/APPZWUr.png - -
2nd tab https://i.stack.imgur.com/6Vogl.jpg
Comment: You could display those inputs (billing add, zip, country etc.) one over the other, as you are doing in the password tab. But both options look good to me, either keeping the 1140px width or making it smaller.
Answer: From your comments on suggested solutions so far, it seems like this layout already works consistently within your sitewide style.
My only recommendation is this (based on how I've created forms in the past) : To better draw users' attention to the form, consider adding a slight gray background shade (#efefef or similar) to the forms (in all tabs), then set the tab container backgrounds to white. If padding is set on or within the form, not on the tab container, the white background only shows through when the form is not full-width. When this particular tab is active, white would be visible to the right of the form.
This would create a visual cue to the user that the form width is intentional. Also, grey color behind white form inputs is more visually attractive than white-on-white. If this looks off to you, though, keep the original. My suggestion may not look good, since you are already using grey as the background behind the tabs. Users expect consistency, and that's what you've given them. Good luck!
Answer: You can horizontally arranged three field, or a hand-drawn map is put in a blank area, in addition I think change the password and account to use the TAB is not reasonable.
Answer: If you prefer the form to use some more horizontal space, you can also consider placing the labels left of the fields. While there are some drawbacks to this (this article sums up the pros and cons nicely) your labels are somewhat of the same length so it shouldn't be too big of an issue.
Answer: I can suggest to set your inputs in an inner card in two ways:

Accordion to login page of Yahoo!; let inner card at right side and add a note in left.
Accordion to login page of Google; let inner card at middle.


Add drop down list / combo box into excel cell

Question: How would I add a drop down list (or combo box) into a cell on Excel 2010?
Comment: Yes, or drop down list, ver 2010.
Comment: I edited your question. I suggest you try a [Google search](http://www.google.co.uk/search?ie=UTF-8&oe=UTF-8&sourceid=navclient&gfns=1&btnI=I%27m%20Feeling%20Lucky&q=excel+add+combo+box#hl=en&sclient=psy-ab&q=excel+add+drop+down+list+2010&oq=excel+add+dro&gs_l=serp.3.2.0l4.2457.2836.0.4618.104.22.168.0.0.1.676.936.0j2j5-1.3.0.les%3B..0.0...1c.1.K5HZORigNkk&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=a1937293c9c50b24&biw=1280&bih=903). This link currently has video and official Microsoft guides
Answer: Usually the simplest way to achieve that is to:

prepare the list next to your table or on other spreadsheet (just input all available values in a column) - it'll be a source for your list of values and it may be hidden later, if you want
mark a cell (or a range of cells) in which list should be displayed
select Data > Data Validation > Data Validation
select Allow: List
indicate the list prepared before as a Source
confirm

The drop-down list is ready. For combo-box you should use VBA, I believe. But you may also use the method described above and e.g. prepare just two-elements list containing "Yes/No" or "True/False", which is generally the same.
The method should work regardless of Excel's version.
Answer: Found this answer when looking to do the same thing myself, while experimenting discovered, there's a second option which means you don't need to use a defined cell range. Entries can be added directly to Source.

Select all the cells you want to have a drop down box
Click > Data Validation
Allow > List
In Source enter any values you want separated by a comma.
Answer: Example:
This example will create a vertical range of 10 cells in which each cell can be filled from values selected from a drop down list which will appear in each cell.
Setup:
Select or insert a blank sheet into a workbook.
Add the following letters to the associated cell locations.
A in cell C1
B in cell C2
C in cell C3
D in cell C4
Select the cells A1 to A10
Within the Ribbon Bar, select 'Data, Data Validation, Data Validation'
    Within the resulting dialog box, select the Settings tab.
    Within the Settings tab select the following 'Validation criteria:'
        Allow: List
        Uncheck Ignore blank
        Enter C1:C4 for the Source:
    Select OK
With your mouse select a cell in the range of cells A1:A10.
A drop down arrow will appear next to any of the cells in the range A1:A10.
The dropdown arrow will not appear in any other cell in the sheet.
Demonstrate:
Demonstrate the results by selecting various entries in the cells within the range A1:A10.


Strumming playing down and up

Question: can anybody help how to identify strumming when to play down and up?
When I hear a song and then play it I never know when to strum down and up, how many times etc. I just cannot hear it.
I spend hours trying different ways and only confuse myself.
Any tips/ideas what to do?
Comment: I suggest to edit the question and add the following details: 1. Is the question about guitar or another instrument? 2. Do you ask about strumming with fingers or a pick?
Answer: The basic strum pattern derives from strumming down on the 4 beats of a (4/4) bar, with the upstrums on the half beats in between. Those have to happen, otherwise, your hand is still in the underneath position! There are times when the down strums are missed, but need to be made off the strings, similarly with the upstrums. So consider a bar of 4/4, there will be 8 strums, 4 down and 4 up, but some will be 'ghost' strums when the strings are not strummed at all, but the hand needs to be shifted to the optimum position for the remainder of the bar.
There are occasions where everything is doubled up, with 8 down (and obviously 8 up strums), and it's very unusual for every movement to produce a sound - hence ghost strums. Very occasionally, everything is inverted, to produce a more pronounced 'offbeat', maybe in reggae, for example.
Answer: To piggyback on the previous answer, and also speaking from playing mandolin, there are different patterns for up and down strumming. For example, there is the Bach-type of strumming, which can go 1D-2D-3D-4D-5D-6U. Just based on what I have seen so far, it is one factor you can use in determining how you want to interpret a particular piece.

Strumming playing down and up


Is there training offered for those interested in being moderators?

Question: Is there training offered for being a moderator? I would love to be one of them. I like learning and helping too.
Answer: What channel would you like to be a moderator of? Eg web forums, Telegram, user/tech support, discord, github, catalyst etc
With stackexchange you can start answering questions and helping out right away. As you gain more reputation points for helping out then more options/access becomes available to you.
A lot of information will need to be self-taught via official blogs, and community websites/channels.
I suggest that you start with the IOG technical discord server and find the area of interest to you and expand out from there.
IOG Technical Discord = https://discord.gg/SNvzGjAj
There are also IOG/IOHK blogs (https://iohk.io/en/blog/posts/page-1/) and email newletters for the different areas eg firstname.lastname@example.com sends out updates relating to stake pool operator interests.
Take a look at the IOG blogs and then you can pick an area of interest to sign up to and then approach them to get more involved.
Comment: Thanks. Am interested in plutus


I hate contests. How can I avoid them?

Question: There's nothing worse to getting home, turning on the radio, and being unable to find a clear frequency that isn't full of a bunch of meaningless QSOs where somehow everyone is 599 and no one has anything to say. Are there any designated "contest-free zones", or other ways I might be able to enjoy amateur radio without contests?
Comment: Welcome, Lee! Unlike a typical chat-style forum site, our goal is to create a database of high-quality [answers](https://ham.stackexchange.com/help/how-to-answer) to questions. This is not a chit-chat site, though we do have chat rooms.
A [comment on a question](https://ham.stackexchange.com/help/privileges/comment) should be discussing how to clarify the question. A comment on an answer should be discussing how to improve the answer. :-)
Answer: Most countries follow the band plans that disallow contesting on WARC frequencies, which include three narrow slices of shortwave frequencies at 30M, 17M, and 12M. If you stick to these frequencies you will rarely, if ever, be bothered by contests.
It's a small slice of spectrum though, so you might simply consider doing what some amateurs do and simply note the days the contests are operating, and plan activities other than amateur radio on those days. Given that most contests are short duration, occur mostly on weekends, and don't occur more than a few times a year, it's not unreasonable to simply avoid affected bands on affected days.
Comment: I'm not interested in football, but living about 8 miles away from [Michigan Stadium](http://en.wikipedia.org/wiki/Michigan_Stadium) over the years I've noted when the home games are specifically to avoid trying to drive around during the day due to the traffic congestion 115 thousand travelers cause several times a year during their season.
Comment: Many contests are just one mode: CW, SSB or RTTY.  So on a big SSB contest weekend, it might be a good idea to work on your brass pounding skills, or visa-verse.  RTTY contests don't tend to choke the bands in the same way, so you can more or less ignore them unless RTTY is your thing.
Comment: ... and CW operation easily going up to digital & SSB area, at least during big contests like CQWW... and the other way around during SSB contests. But it is only a few days a year, most hams can probably live with that.
Comment: … although you may find an RTTY contester occasionally straying into PSK31 areas during contests.
Answer: One of my approaches to avoiding contests is operating on the opposite end of the band. During a big contest weekend it can be tough to avoid, when calling CQ, and someone comes back with ID and contest requirement, so the best thing to do is find the extremities of the band. Usually it's the upper end of the band, like for instance on 20 meters, I'll just call CQ in the 14.330 MHz to 14.350 MHz area. It's generally quiet there, and I have found that most call backs are other hams looking to rag chew. Like an earlier answer pointed out, just avoid the traffic by going around it.
Comment: I think it'd be best to move on from this conversation and focus on the OP's question. Further conversations can be held in chat if desired.
Comment: It might be quiet because it's out of band.  In all ITU regions, 20m runs to 14.350.  Though if you change the 4s to 3s in you answer, the point is well taken. Though, being USB you need to leave room as you approach 14.350.
Comment: If your rig uses more bandwidth when you turn the power up, it's definitely not operating correctly. QRP should have nothing to do with the bandwidth you use, and I think the point he was trying to make is that if you have the dial set to USB and 14.350 MHz, you are going as much as 4 kHz out of band, QRP or not.
Comment: @MichaelKjörling I know this. Why has this become an attack on my ability to legally operate? I'll have you know, that I operate within the parameters of my licensing. I was just answering a question. I don't understand how what you guys are telling me helps the OP resolve his question.
Comment: Yes, thanks for pointing that out. Those were typos. As far as 14.350 goes, I primarily operate QRP, so I generally don't notice too much bandwidth spillover, I think my point being is that 14.330 to 14.350 MHz is a good area of operation for avoiding contesting jam ups. There is no suggestion of intentional illegal operation going on over here =)
Comment: Like I said I don't notice too much bandwidth spillover. If my radio is above 4kHz bandwidth, No one has ever reported that to me. Besides this doesn't really address the original question. Some hams say it's okay to operate within 3kHz of band limits. Anyhow, I was pointing out the range not suggesting that the OP use the specific frequency 14.350MHz. Irrelevant!
Comment: @ChrisWalsh It is your own responsibility to ensure that your transmission at no time happens to be outside of the frequency range within which you are legally authorized to transmit.
Answer: Apart from the WARC bands, you could possibly try CB radio. I know in the US it usually has a negative stigma attached to it; but a lot of my local HAMs are similar to you, as in they hate contests, so they go on CB channel 38 when they can't get through on the other HF bands.
10m doesn't get used very much here, and even if it does, we get horrible QRM, so 11m (CB) is the last resort.
However, if you want to be a 'reckless' ham, you could always transmit voice over the CW and data frequencies. People might hate you for it, but It's not illegal, at least not here (UK).
Comment: Understandable. I shall try to keep that in mind in the future. That's for pointing that out :)
Comment: But in the US, where it was originally asked, it is illegal.
Answer: I strongly disagree with such kind of well known, instant answers (myths) that contests are short and rare, use WARC band instead, you can participate them with small power and antennas anytime to make more shiny DX's, and all because they are arrogant in their senselessness despite of any amount of goodwill. I know that I am in the minority with this opinion but I feel it important to express, that's why I spend time to note them. Some competing can be fun and useful but contesting on "higher levels" is a wrong, instinctive, and underregulated approach to the radio amateur principles, namely the learning, building and experimenting. Ham radio is not a sport, it is intended to be much more competent. There can be compromises but in this topic you asked how to avoid them, and it signals something... Even some hams with very big antenna farms declare on their web pages that they are not interested in contesting but DX-ing.

Other radio amateurs have absolutely no right to send you somewhere else from our precious collective resources called ham bands that you are licensed to use to another ham band or segment. Nothing can justify it. Why? E.g. because somebody might have a radio or an antenna only for that very band, or only for the classic bands (not for WARC bands), etc., you can imagine. What you see instead? In the last years, even the IARU recommendations miss the lowest 10 kHz sections of bands those are traditionally for DX-ing. Also, the important calling frequencies, like QRP or other mode's calling frequencies (those should have an absolute priority) are completely surrounded by the recommended stretches of the contests. That's insane (regarding to the average level of discipline of ham folks).

Many (most!) weekends are full with contests, and stations on steroids, at least here. They take every space because "the contest needs it", and you must obey. There are exceptions as everywhere, though. I respect the technical aspects but small stations are completely unable to make a single QSO many times at weekends when most of the people have a little time for the hobby. There is no place, therefore and mostly there is no partner. There are even larger pile-ups on DX's you can't penetrate since that is a contest and there are tons of kilowatts in the ether (even if tons of kilowatts is not an SI unit, hi).

There are incomplete reports in QSO's. What is in my license? Sending-receiving the RST's are obligatory just like logging the frequency. It is true at least in my country, but it is a tradition as well, anyway. What is in the contest logs? Always 599 or 59. Because "the contests need it this way"... It is only an agreement, not a necessity. And they go further: some contests got rid off of the RST's at all. But, to say something good, too: on V/U/SHF, where contesting is much more acceptable, there are real RS(T) reports. Such contests are usually much closer to the ideal ham activities including technical aspects as well.

Do not forget: if you make contest QSO's, it is a bad manner not sending at least a control log, so that could be the next thing you did not want...

Let me say again that I understand the compromises, I also take part of contests from our club stations (because those are the events having enough gravity to collect people to one place), but I'm rather displeased with the general attitude toward the small but equally important cultivators of this hobby, the wrong priorities and wrong habits. I don't think the marked answer is the real one for you.
Comment: This does not provide an answer to the question. Once you have sufficient [reputation](https://ham.stackexchange.com/help/whats-reputation) you will be able to [comment on any post](https://ham.stackexchange.com/help/privileges/comment); instead, [provide answers that don't require clarification from the asker](https://meta.stackexchange.com/questions/214173/why-do-i-need-50-reputation-to-comment-what-can-i-do-instead). - [From Review](/review/late-answers/12508)
Comment: I was counting on such reactions; my answer does provide useful information. My answer is, hardly achievable or not: you shouldn't go elsewhere, use the band you wanted to work on, stand up for using them by our best traditions, and I mentioned one important possibility: (at least the lowest some kHz's of the) lowest 10 kHz sections are still respected more or less to leave them free. Btw. I realized too late that this is a very old question on StackExchange, so never mind. :-)

I hate contests. How can I avoid them?


Solve $y^3=x^{3}+8x^{2}-6x+8$ for positive integers $x, y $

Question: How we can solve this equation :  $$y^3=x^{3}+8x^{2}-6x+8$$ for positive integers  $x, y $?  I tried to factories the $L. H. S $  but I couldn't complete the solution. How I can solve it?  Thanks.
Answer: Since we have$$\begin{align}&(x+2)^3\lt x^3+8x^2-6x+8\lt (x+3)^3\\&\iff x^2-9x\gt 0\quad\text{and}\quad x^2+33x+19\gt 0\\&\iff x\gt 9\end{align}$$
we know that if $x\gt 9$, then there is no such positive integer $y$. So, we have $x\le 9$.
Now, all we need is to check if each of $x=1,2,\cdots,9$ is sufficient.
Thus, we know that $(x,y)=(9,11)$ is the only solution.
Comment: @rugi: I just wanted to get integers $a,b$ such that $(x+a)^3\lt x^3+8x^2-6x+8\lt (x+a+1)^3$ is true for all $x\gt b$. Then, noting that the coefficient of $x^2$ is $8$ in the middle polynomial, we can see that $a$ has to be $2$, and so on. I hope this helps.
Comment: Nice Solution. But I have a question. How to invent $$\begin{align}&(x+2)^3\lt x^3+8x^2-6x+8\lt (x+3)^3\\&\iff x^2-9x\gt 0\quad\text{and}\quad x^2+33x+19\gt 0\\&\iff x\gt 9\end{align}$$ in exam setup. Is it a result of experience gained from massive number of problem solving or you have used some other insight to arrive it which in final solution you have omitted? In short can you please elaborate your thought process. Thanks in advance.
Comment: Thanks. It is now clearer. But why to think of restricting between $(a)$ and $(a+1)$. I mean to say why not $(a)$ and $(a+k)$ where $k$ is any integer? I hope I am not asking something really silly.
Comment: @rugi: Because $(x+a)^3$ and $(x+a+1)^3$ are **consecutive cubes**, which is the key of this answer. As we can have $(x+2)^3\lt x^3+8x^2-6x+8\lt (x+3)^3$ for all $x\gt 9$ where $(x+2)^3$ and $(x+3)^3$ are consecutive cubes, if $x\gt 9$, then $x^3+8x^2-6x+8$ cannot be a cube, which means that there is no integer $y$ such that $y^3=x^3+8x^2-6x+8$ as written in the answer.
Answer: It's clear by inspection that $x$ and $y$ must have the same parity, so let's write $y=x+2k$.  The equation reduces to a quadratic in $x$:
$$(4-3k)x^2-3(1+2k^2)x+4(1-k^3)=0$$
The discriminant of this quadratic equation is
$$\begin{align}
\Delta(k)&=9(1+2k^2)^2-16(4-3k)(1-k^3)\\
&=-(12k^4-64k^3-36k^2-48k+55)
\end{align}$$
For the quadratic to have any real (much less integer) roots, $\Delta(k)$ must be non-negative.  This clearly restricts $k$ to a finite interval, which turns out to be $1\le k\le5$.  (It's easy to see $\Delta(k)\lt0$ if $k\le0$. The verification that $\Delta(k)\lt0$ if $k\ge6$ is little messy, so I'm omitting it.  However, you can, if you like, skip from here to the "added later" section below.)
For the quadratic to have any integers roots, $\Delta(k)$ must be a square, so at this point it's easiest to just calculate:
$$\begin{align}
\Delta(1)&=81\\
\Delta(2)&=505\\
\Delta(3)&=1169\\
\Delta(4)&=1737\\
\Delta(5)&=1585\\
\end{align}$$
The only square here is when $k=1$, so we see the quadratic
$$x^2-9x=0$$
which has roots $x=0$ and $x=9$.  Thus the only solution in positive integers is $(x,y)=(9,11)$, and the only other solution in integers is $(x,y)=(0,2)$.
Remark:  This solution and mathlove's are quite different, but they both lead to computing a small number of cases (nine in mathlove's, five here).
Added later:  I got to wondering if there's some easy way to avoid doing a case-by-case computational check.  It turns out there is, at least if you restrict to $x\gt0$ (which is specified by the OP).
Starting from the observation that $k$ must be positive in order for $\Delta(k)$ to be non-negative, let's go back to the quadratic in $x$ and rewrite it as a cubic in $k$:
$$4k^3+6xk^2+3x^2k-(4x^2-3x+4)=0$$
Thinking of the left hand side as a function $f(k)$ (holding $x$ constant), note that
$$f'(k)=12k^2+12xk+3x^2=3(2k+x)^2\ge0$$
Consequently, if $k\ge2$,
$$\begin{align}
4k^3+6xk^2+3x^2k-(4x^2-3x+4)&\ge32+24x+6x^2-(4x^2-3x+4)\\
&=2x^2+27x+28\\
&\gt0\qquad\text{if }x\gt0
\end{align}$$
This leaves $k=1$ as the only possible (integer) value that allows for a positive integer value of $x$, which turns out to be $x=9$ (hence $y=11$).
Comment: @user256952, no, you didn't miss anything.  It was really just a remark, in case anyone wondered if the equation had any non-positive integer solutions.  (For some problems, restricting to positive integers is crucial, in terms of finding a simple solution, while for other problems it isn't; this problem is of the latter variety.)
Comment: Nice solution sir. but I think we will refuse t$(0, 2) $ because we want to solve the equation for $\large{positive}$ integers $x, y $... or I missed something?
Comment: I love this solution because it is more illuminating than the previous answer.


Which d orbitals are involved in "d3s hybridisation"?

Question: I was reading about hybridisation and came across a point saying that $\mathrm{d^3s}$ hybridisation involves only $\mathrm d_{xy}$, $\mathrm d_{yz}$, and $\mathrm d_{zx}$ orbitals and not $\mathrm d_{x^2-y^2}$ nor $\mathrm d_{z^2}$. Why is that so?
Comment: Please read https://chemistry.stackexchange.com/questions/76726/why-is-it-wrong-to-use-the-concept-of-hybridization-for-transition-metal-complex
Comment: @NisargBhavsar But CrCl4- has Cr(+3) which is d3 so only two d orbitals are free, and you can't get d3s. Hybrdisation theory is good for main group elements; for transition metal complexes, it's not accurate and often gives wrong predictions or explanations. It has been mostly superseded by MO theory.
Comment: @HarryHolmes Yes, that's the one exception, and that's why I kept it as such in the original post.
Comment: What is d3s hybridisation and in which compound have you seen it?
Comment: @NisargBhavsar [MnCl4]- has Mn(+3) which is $\mathrm{d^4}$. I don't think d3s hybridisation is possible, it has to be sp3. Besides, hybrdisation is not useful for transition metals complexes.
Comment: Please note that the labels of the d orbital are not $x - y$, etc. they are $xy$. Products, not differences.
Comment: @orthocresol, the other ones are fine, but [wikipedia](https://en.m.wikipedia.org/wiki/Atomic_orbital#Shapes_of_orbitals) (see the orbitals table) says it's $d_{x^2-y^2}$. Sorry if it's stupid; I don't really know how the orbitals actually come about anyway.
Answer: First off, I'll reiterate what's mentioned in the comments - that hybrid orbitals are not a particularly good approach for transition metal complexes. But with that said, if you are going to apply this approach to a tetrahedral transition metal complex, here's how it works. For simplicity, I'm going to assume that only sigma bonding is relevent. You can do the same analysis including pi bonding, but it's more complicated.
Short answer: only the off-axis d orbitals have the right symmetry to match the ligands in a tetrahedral point group.
Long answer: The mathematical basis for constructing both delocalized and localized hybrid bond orbitals comes from group theory. If you haven't gotten to group theory in your studies, this explanation might not make a lot of sense, but at least you'll have to starting point to look deeper.
A tetrahedral molecule with four identical ligands is said to be in point group Td, which is just an abbreviation of "tetrahedral". Every point group has symmetries associated with it based on what operations can be performed that return the original structure. In point group Td, these are named A1, A2, E, T1 and T2.
When we build molecular orbitals, we combine the orbitals on the four ligands and look for possible symmetry groups. Then we look at the symmetry of the orbitals on the metal center and match the metal orbitals and "ligand group orbitals" based on symmetry. (An alternative approach is to look at the symmetry transformation of the bond vectors, which is described here: https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Modules_and_Websites_(Inorganic_Chemistry)/Advanced_Inorganic_Chemistry_(Wikibook)/01%3A_Chapters/1.09%3A_Td_Molecular_Orbitals. The result is the same.)
Making a long story short, the tetrahedral ligand group orbitals for a sigma-bonded complex fall into two symmetry groups. One orbital, in which all four ligand orbitals have the same phase, is A1. A second group of three orbitals in which the ligand orbitals are pairwise in opposite phases matches the T2 symmetry of the Td group.
On the metal center, our valence atomic orbitals are 4s, 3d and 4p. The 4s orbital matches the A1 symmetry, while the 4p and 3d (xy, yz and xz) match the T2 symmetry. The 3d(x2-y2) and 3d(z2) orbitals, on the contrary, match the E symmetry from group Td. Since the E symmetry doesn't match either of our ligand group orbitals, we can't use these two orbitals for bonding.
Since the 4s orbital is the only match for the A1 symmetry, we must involve that orbital in bonding. For the T2 symmetry, however, we have two choices. We can either use the three 4p orbitals and ultimately make four sp3 hybrids, or we can use the three T2 symmetry 3d orbitals and end up with d3s hybrids. The sp3 hybridization is much more familiar to most people because they have learned it for organic compounds such as methane, but that's not the right choice here. If we consider the relative energy levels of the orbitals on a transition metal, we see that 3d is lower than 4p and so is closer to the ligand orbitals (which are lower in energy than both). Furthermore, the off-axis d orbitals are pointed more directly at the ligands in a tetrahedral complex (which are also off-axis), so this intuitively makes more sense as well.
Finally, to your question about $\ce{CrCl2O2}$, that molecule belongs to point group C2v, so you can apply the analysis above to that point group to get the allowable hybridizations in the same manner as for the Td case.
Comment: @ShoubhikRMaiti That's only half true. The orbitals are indeed degenerate in the absence of ligands, and the axes in that case are completely arbitrary, but as soon as we assign a point group, that designation is done with respect to specific axes related to the symmetry operations, so the axes are no longer arbitrary. And we have specific conventions for coordinate systems of molecules that are used in group theory, so proper application of convention will always yield the same three d orbitals in the T2 group.
Comment: +1 But I would also add that the choice of which 3 d-orbitals are used for hybridisation, is entirely dependent on the choice of axes. In a free atom, all 5 d-orbitals are degenerate. It is only when you bring in the ligands and choose the x y z axes that you get a differentiation.
Comment: Yes, but hybridisation is not usually taught with symmetry arguments. My point is that, if someone started reading hybridisation and asked why those 3 d-orbitals are used, the answer should be that it's because of the choice of axes. The choice of axes is a convention but convention in itself is arbitrary. Any three perpendicular axes could be chosen, but one of them has been decided to be the right one and that's an arbitrary choice.


I once stole something but I don't know who it belonged to so how do I seek forgiveness for it?

Question: I once stole a piece of clothing in the hostel. I don't know who did it belong to. I don't know the owner. It's been years now. I have realized my sin and have repented to God. Cried and promised never to do such thing again. But since it's transgression against another human being so how do I fix it? I don't know the person. And there's no way I can find them. Is there anyway to compensate for it?
Comment: Does this answer your question? https://islamqa.info/amp/en/answers/43017
Answer: In Islam or in any other religion or from good manners perspective the solution is first to ask Almighty Allah for Forgiveness, second try not to do it again, last but not least, make a charity with the approximate price or value of the thing you took and whish this good fact to the person who owns what you took from him/her.
تصدق بقيمة المأخوذ و انوي ذلك صدقة لصاحب أو صاحبة المأخوذ.
This advice is for me, for you, for everyone. Everyone is the one at fault but the good one is who keeps asking Allah for forgiveness and trying again and again and infinitely to avoid doing bad things. That's the real point. stay safe


Linear regression with low variations in the explanatory variables

Question: Below is a scatter plot of some data with the best fit OLS line. From $R^2$ we can see it is a quite a poor fit. But is there a way to predict before running the regression that the results won't be reliable? My gut-feeling is that because we've got the cluster of data points on 1.5, 2 and 2.5, the linear regression is not a good model. But I am looking for a more formal explanation.
Comment: Note that there is a single data point at X = 3.5, and 8 or 9 data points at X = 1.5 (for example). This has the effect of weighting the data *away* from the high end. I suggest making a test using the average value where there are multiple data points with the same X value, and see if that might work better for your modeling needs. My eyeballing the data indicates a straight line will not be a good model in such a test, and @NickCox's suggestion of using a quadratic (or even cubic) seems wise.
Answer: You're asking several different questions.

Why the predictor takes on particular distinct values (multiples of 0.25, it seems) could be an important detail. Ideally you would have information on why that happens from the data source or from a client or boss, say that the numbers arise from division by 4 and there is a good reason for that. At worst, even with no detail on that point in this case the number of distinct values still seems large enough to detect an overall pattern.
Calling $R^2 = 0.5306$ quite poor may or may not be echoed by people who know about the data in that field and what to expect. There are fields where anything less than say $0.9$ could mean nothing but disaster. There are  fields where anything higher than that means a bogus or even tautologous relationship (just two different versions of the same underlying variable) or fraud, because correlations just aren't that strong otherwise.
To my eye, the scatter suggests curvature, so I would try a quadratic next. I would also want substantive detail on whether a relationship with a turning point makes sense and also on whether the response can ever be negative.
One way to tell how well a regression will work when there is just one predictor, or you can plot in two dimensions as here, is to look at the scatter plot. Otherwise I don't know what kind of prior analysis you're reaching for.
Reliable in many statistical contexts means reproducible rather than strong. A reliable relationship will show up in similar form in a similar sample.

I don't think that there is much scope to find good models without context on the data and how they arose.
Comment: +1.  But in this particular a case a quadratic will work only poorly.  A spline might be a better choice for many applications, or even settling for treating the discrete regressor values as categories.  A direct answer to the stated question is "yes, it's obvious a linear fit will be poor, because the differences between the conditional means and any line are greater than the conditional standard errors."  In other words, a standard goodness of fit test will provide the formal answer that was requested; and from the scatterplot alone one can readily *see* what the test will result in.
Comment: @whuber "poorly" is a little strong, not least because splines aren't to everyone's taste and from the tone of the question would possibly be more complicated than the OP might prefer. I'd like to see the data to compare different ideas. By eye a quadratic would have turning point around $x = 2.75$. I'd also like to know whether the data should honour $(0, 0)$. The dopey axis titles "Axis Title" almost look like wilful attempts to obscure what the data represent! .
Comment: @NickCox, I am afraid I cannot share the data, as you have guessed. But I appreciate your insight.
Comment: Well, in principle, someone can could digitise your graph and get very close to your real data. So, if your data are confidential you shouldn't even show a graph. I remain puzzled that you expect good advice when you can't give out very much real information. That's a situation in which you need to hire a consultant within a non-disclosure contract.


Is my proof correct? m×n complex matrix A*A is invertible iff A has full column rank.

Question: I am a high school student in South Korea. I am currently learning Linear Algebra in school. In this question, $A^*$ means conjugate transpose.
I am wondering if this sentence is true or false. [m×n complex matrix $A^*A$ is invertible iff $A$ has full column rank.]
If A is real, it is true and the proof is simple. Since $null(A^{T}A)=null(A)$, $rank(A^{T}A)=rank(A)$ so $A^{T}A$ is invertible iff A has full column rank.
Is it okay if I use this result directly in complex field?(Assuming standard inner product in a complex field, $A^*Ax=0 \implies x ^* A ^* Ax=0,||Ax||^{2}=0\,\,Ax=0$ so $A ^* A$ and $A$ has the same nullspace, and so on. ) Or if there is a counterexample, please tell me. $%(I don't know why the conjugate transpose expression is not working with mathjax in my computer.. sorry)$
Comment: A is m×n complex matrix, A*A is invertible iff A has full column rank, is it true or false?
Comment: Note that $A^*A$ is always square, even if $A$ is not.
Comment: Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
Answer: Yes, the statement holds and the idea behind your proof is correct. Here is one complete version of the proof.
If $A^*A$ is invertible, then
$$
Ax = 0 \implies A^*Ax = 0 \implies (A^*A)^{-1}(A^*A)x = 0 \implies x = 0,
$$
which means that the columns of $A$ are linearly independent, which means that $A$ has full column rank.
Conversely, if $A$ has full column rank, then we find that
$$
A^*Ax = 0 \implies x^*A^*Ax = 0 \implies (Ax)^*(Ax) = 0
\\\implies \|Ax\|^2 = 0 \implies Ax = 0 \implies x = 0.
$$
Thus, $A^*A$ is a square matrix with linearly independent columns, which means that $A^*A$ is invertible.


Minecraft - Piston elevator without Sticky/Slime/Ender Pearls?

Question: I need a vertical elevator that does not use sticky pistons, slime, or ender pearls. I need to go up around 30 blocks with one press of a button or lever. How can this be done?
Comment: What result do you expect? Something fancy with minecarts or boats or maybe even a command block solution?
Comment: Just a simple and/or compact elevator that moves the player up many blocks with a single press. I'd like to not use boats or water, mainly pistons if possible.
Comment: like [this one](https://www.youtube.com/watch?v=obGjqdMOJ9s)?
Answer: Minecraft 1.13 (The Underwater Update) added a new feature that makes elevators easier than ever. You don't need pistons, slime, ender pearls, or even redstone!
All you need is water, soul sand, and magma blocks. Both can be acquired from the nether, and magma blocks now spawn naturally in the oceans. If you have a column of water source blocks (not flowing water blocks - they MUST be a water source block) with soul sand beneath, it'll create a jet of bubbles that pushes you and all other entities upward. Similarly, if you have a column of water source blocks with a magma block at the bottom, it pulls you down. You can tell if they're working because there will be bubble animations inside the water. It also doesn't consume your air meter, so you can hang out in the flooded "elevator shaft" and not drown. You can learn more about them on the wiki. It is now possible to create elevators that have a 1x1 footprint on the ground, and go arbitrarily tall, with no moving parts whatsoever.
If you want to get fancy with redstone, you can use pistons to push magma, soul sand, or another block type under the column to switch whether it goes up, down, or nowhere, but that is beyond the scope of your question.
Answer: Have you seen this tutorial?
It shows you a bunch of good elevators and how to make them. As of the needs you described, I would reccomend looking at the 4th elevator. It uses pistons and redstone, but no sticky pistons or slime.

If you want to look at the showcase and the tutorial and nothing else, you can skip to:

•Showcase: 02:25

•Tutorial:      16:16
Answer: Use stairs! When a stair block is pushed under your character, it climbs up if you are in a 1-block space (It does this by pushing you up against the wall) You should have delays as it goes up.
Comment: but this uses sticky pistons which he doesn't want
Comment: There are youtube videos on this too.
Comment: I also heard this method can result in death which in Hardcore to me is a bit scary.
Answer: Here is one that uses pistons and redstone, but it does not use any sticky pistons:

You can get even more ideas here.
I hope I have been helpful.
Comment: Thank you for your reply but I have checked out other elevators but I kind of really want a piston elevator. I'm sure one is possible but I haven't really found a way to do a piston elevator without sticky pistons. Do you have any alternative ideas for survival mode?
Comment: Please don't just present options; customize your answer to solve the problem the asker has posed.


Linear dependence and linear independence of functions in linear algebra

Question: I am trying to understand linear dependence and linear independence of real valued functions on a set. Say S.
 I want to know that using wronskain how can we say that a set S of functions is linearly dependent. I was thinking that if wronskain is zero everywhere on the domain then S is linearly dependent and if at least at one point of the domain wronskain is nonzero then S is linearly independent. Where is the problem actually ?
Comment: No. Wikipedia give a counterexample of wronskian being 0 but the functions are not linear dependent. Gate: [this](https://en.m.wikipedia.org/wiki/Wronskian)
Comment: Thank you. I noticed that. Will you please tell me that in wiki it is written that " the Wronskian can be used to show that a set of differentiable functions is linearly independent on an interval by showing that it does not vanish identically. It may, however, vanish at isolated points" does it mean it can vanish at most at isolated points?  If I say it vanishes everywhere except an isolated point then still set will be linearly independent.  Am I doing right?
Answer: Let us see the relation between the Wronskain and the linearly dependent and independent solutions. It may be clear your confusion.
Let $f$ and $g$ be two real valued differentiable functions on a set $S = [a,b]$ (say). If Wronskian $W(f,g)(t_{0})$ is nonzero for some $t_{0}$ in $[a,b]$, then $f$ and $g$ are linearly independent on $[a,b]$.
If $f$ and $g$ are linearly dependent then the Wronskian $W(f,g)(t_{0})$ is zero for all  $t_{0}$  in [a,b] .
You can also verify this in

"Differential Equations" by Shepley L. Ross ($3^{rd}$ Edition, Page 112, Theorem $4.4$).
"An Introduction to Ordinary Differential Equations" by Ravi P. Agarwal, Donal O'Regan (Page $118$ (Theorem $17.1$))


In John 4, why does Jesus say he was not honored in his own country yet he was welcomed?

Question:
"For Jesus Himself testified that a prophet has no honor in his own country. So when He came to Galilee, the Galileans received Him, having seen all the things He did in Jerusalem at the feast; for they also had gone to the feast."
John 4:44-45 NKJV
Answer: There were indeed many in Galilee who believed in Jesus.
The point made in multiple Gospel accounts is that the people around whom Jesus grew up struggled to see Him as more than just the carpenter's son.
From Luke 4:

14 And Jesus returned in the power of the Spirit into Galilee: and
there went out a fame of him through all the region round about.
15 And he taught in their synagogues, being glorified of all.
16 And he came to Nazareth, where he had been brought up: and, as his
custom was, he went into the synagogue on the sabbath day, and stood
up for to read.

Luke then proceeds to record Jesus' teaching and the reaction of the people present, including:

22 And all bare him witness, and wondered at the gracious words which
proceeded out of his mouth. And they said, Is not this Joseph's son?

(note that the community thought Jesus was Joseph's son)
Mighty as Jesus was in word and deed, many could not get over the fact that someone they had known as a child could be anyone significant. Most people from other Galilean communities didn't know Jesus as a child and so wouldn't have this struggle.
This is a very insightful observation about human nature--we're often willing to see strangers as great and wonderful people--but those we know up close we tend not to grant the benefit of the doubt.
Answer: Let us be clear about what Jesus did say in Matt 4:44 -

For Jesus Himself testified that a prophet has no honor in the own
hometown (= Nazareth).  [See also Luke 4:24]

Jesus then was received positively in Cana - quite separate from Nazareth where he was rejected (Luke 4:28-30).
Jesus was also received positively in Capernaum (Luke 4:23), again, quote separate from Nazareth but still in the region of Galilee.
Answer: Those closest to Jesus, who grew up with him, had the most trouble respecting him.

 After this Jesus went about in Galilee. He would not go about in Judea, because the Jews were seeking to kill him. 2 Now the Jews' Feast of Booths was at hand. 3 So his brothers said to him, "Leave here and go to Judea, that your disciples also may see the works you are doing. 4 For no one works in secret if he seeks to be known openly. If you do these things, show yourself to the world." 5 For not even his brothers believed in him. 6 Jesus said to them, "My time has not yet come, but your time is always here. 7 The world cannot hate you, but it hates me because I testify about it that its works are evil. 8 You go up to the feast. I am not going up to this feast, for my time has not yet fully come." 9 After saying this, he remained in Galilee.
(John 7:1–9, ESV)

It was the same where he grew up in Nazareth.

 They said, "Is not this Jesus, the son of Joseph, whose father and mother we know? How does he now say, 'I have come down from heaven'?"
(John 6:42, ESV)

In wasn't until his death and resurrection that his brothers decided to believe Jesus.

 But motioning to them with his hand to be silent, he [Peter] described to them how the Lord had brought him out of the prison. And he said, "Tell these things to James [Jesus' brother] and to the brothers." Then he departed and went to another place.
(Acts 12:17, ESV)

James, the apostle, the brother of John, had been executed (Acts 12:1).
There is also a difference between welcoming someone and honoring them as a prophet.  Just because his brothers didn't believe him doesn't mean they wouldn't welcome him.


Support for EIP1271 smart contract signatures for 0x nft swaps?

Question: Does 0x's nft swapping protocol plan on supporting eip 1271 smart contract signatures for the new nft swap protocol? We want to use gnosis safe (multisig) and other smart contract wallet (argent) to bid and sell nfts on 0x
Answer: For smart contract order makers, you will want to use the presigned/on-chain orders pattern. See: https://docs.0x.org/nft-support/guides/signing-orders/on-chain-orders
Comment: what about for buying? i.e. a multisig/safe *buying* an item that has been listed
Comment: Buying an order doesn't require a signature from the taker.


Copying column from excel into sharepoint list

Question: When I look up how to copy a column from excel into a sharepoint list it says that a simple copy paste should work. When I do this however it ends up copying all of the values into one cell. Does anyone know why this is happening?
Comment: How are you pasting into SharePoint list? Are you using "Quick Edit" view in the list when pasting?  See here https://sharepointmaven.com/3-ways-import-excel-sharepoint/ how to import excel data into SharePoint list
Answer: Here're some references about how to copy column from excel into SharePoint list for you.
How to Import Excel List Items to an Existing SharePoint List
Here are 3 ways to import Excel data to SharePoint list
Import/Copy/Paste Data from Excel into Existing SharePoint List