Determining the angle theta at the Mohr's Circle

Question: I'm having trouble about deciding the initial angle theta before drawing the Mohr's circle.
From what I've learned from the lecture, I need to draw a normal line of indicated plane and find the angle between the x axis and the normal line. Which gives me 150 degree from the first pic and 115 degree from the second pic. And after that, I need to double these angle to put them in the Mohr's Circle, which is 300 and 230 respectively. But the solution speaks otherwise of problem 17. There weren't any normal line and it just doubled the angle right away. From my point of view, these two situations are conceptually same. I don't understand what's the difference. Any explanations would be greatly appreciated.
Comment: "I'm having trouble about deciding the initial angle theta ..." I don't know what is missing from your mind, as all stresses are given on a block, which is to be rotated 25 degrees. You shall review the examples in the textbook and give the problem a shot. Then ask for help as the last resort.
Answer: There are two different angle $\theta$'s. one is the normal stress angle $\theta_p $between the stress axis, X, and point a(x,s) on the mohr circle.
The other is shear stress angle $\theta_s$ from the shear axis with a positive direction down and the sense of the angle is from the shear axis to point a(x,s).
here is a site that explains how to build the mohr circle. linkhere
'


Magento 2.2.5: Disable Add to Cart button

Question: I'm looking for a solution to disable all add cart buttons on every page in the frontend without using phtml file or CSS.
I've found some solutions but for disabling price, but not add to cart button, I hope to find some solution like this:
How to hide price in magento2

Any idea, please help :) Thanks
Comment: did you follow this [link](https://magenticians.com/magento-2-disable-add-to-cart-button/)? or [this](https://magento.stackexchange.com/questions/113812/how-to-remove-the-add-to-cart-button-from-catalog-pages-in-magento-2) might be helpful to you
Comment: thanks, but this 2 link still use phtml file as well :(
Answer: STEP-BY-STEP PROCESS TO DISABLE ADD TO CART BUTTON IN MAGENTO 2
Please follow the below steps to learn how to disable add to cart button in your Magento 2 store.
STEP – 1
First of all, log in to your admin panel and navigate to Stores > Settings > Configuration.
STEP – 2
After that, click on the Catalog menu option in the Catalog tab, find the Category Permissions section and do the following:
Select YES in the Enable field.
STEP – 3
Next, find the Allow Browsing Category field and set it to either For Specific Customer Groups or Restrict Access & Redirect to Landing Page.
If you select For Specified Customer Groups, then you need to select which customer groups can see products.
On the other hand, if you select Restrict Access & Redirect to Landing Page, you need to select a landing page to redirect non-registered users to.
STEP – 4
Now, in the Display Product Prices field, you need to decide if you want to hide prices from all users or just from the specified customer groups.
STEP – 5
After that, select YES or NO in the Allow Adding to Cart for Specified Customer Groups field to remove add to cart button.
STEP – 6
Next, you can also restrict non-registered users from Catalog Search in the Disallow Catalog Search field.
STEP – 7
Now, save all changes and refresh the cache.
STEP – 8
After that, you now need to apply for the category permissions.
For this, navigate to Catalog > Categories and select a category from the category tree.
STEP – 9
Next, open the Category Permissions section and click on the New Permission button.
Here, set permission details as per your requirements and save the changes to remove the add to cart button for non-registered users in your Magento 2 store.
Comment: thanks for reply, it's been so long, i can't verify this answer at the moment .. sorry :(


How to increase the perception of depth in a flat logo

Question: I am creating a logo with the arch from Cabo San Lucas. Any suggestions on how to make it look like it has more depth?
Answer: You mean simply: More 3D image look, no need to increase the hidden message content or the visual balance of the set-up - OK?
3D look needs a little bit more perspective. The waves should be smaller at further and maybe to have little flatter contrast, too. The horizon line should exist. The rocky island is too dark. You have no room to make the shadows visible enough. Anything small seen as big in the front and something big or same size in the background seen as small helps.
Try to search how others have illustrated the sea and got it to continue to the horizon.
Addendum: This is maybe an overkill because it destroys the simplicity. But it also tells how I think. The name has been thrown onto the water because there is some free space. Now all can be bigger. Contrast has been increased quite much, more in the front. Sorry for maybe trashing your work. Send a comment if you want this off. If something is ok, the original creator can use it as will.
Answer: The illusion of depth is created with highlights and lowlights. Light areas are perceived as being closer to you and darker farther away.
If your main shape is dark you have a challenge. It should be the lighter than its background. Make the sky a gradient from dark blue to medium blue (darker at the horizon) adjust until it looks like daylight sky. The darker you can keep it.
Make the island a gradient side to side - dark brown, light brown, light brown. Or make it light brown with dark brown shadows.
Make the ocean waves closer together as they get farther away. The other important aspect of creating 3D look is perspective, so those top waves should look like they're at the horizon or behind the island.
Answer: Based on your original, I feel like you should go the vintage travel poster route.
https://goo.gl/images/lR9iGn
You can refine the simple shapes you have and use lighting to help get a more "realistic/3d" look. This just adds a little depth without being overly rendered. Another way to think about it is "cell shading" like in animation.
To do this, google pics of El Arco and pick one with clearly defined light and shadow on the rock.
https://goo.gl/images/ZJ04dO
Design your logo similar to as you have but adjust to have one color for light, one for shadow.
As for the ocean, I think it works better as a flat under El Arco with minimal wave detail or as the stylized waves like you have. But make your waves larger as they get closer to the bottom of the icon to imply some depth.


Mountain Biker wanting to change to cyclo or road? Which one?

Question: I ride an inexpensive Trek modified mountain bike and I spend some of my ride on the road and some on the canal, which of course is rather flat. Sometimes at the mid point of my ride I will decide to get off the canal and get onto road with lots of hills. Obviously the mountain bike is not made for this however I enjoy that challenge. Right now I am looking at the Crux Elite EVO. Would that be a good choice, is it worth the money and how much faster would I be on it? Or road bike???
Comment: For several years my only bike was an XC hardtail, but I decided to build a road bike in addition to it. After riding it for a couple of months I can say that I really enjoy the the roadie, so you might have a similar experience.
Comment: I second @Klaster_1, only I went via a FS XC bike in between.
Answer: I've had a hardtail mountain bike for a few years, and used it for all kinds of rides -- singletrack, rail trails, roads.  A few months ago I got a cyclocross bike (Norco Threshold) in addition to the mountain bike.  So I'm in pretty much exactly the situation you describe.
I am enjoying the cyclocross bike and I feel like it's made me about 3-4mph faster.  I am surprised that I like the drop handlebars better (more comfortable) than the straight handlebars on the mountain bike.
I already had a set of slick tires for the mountain bike that I installed for road rides, and switched back to knobby tires for singletrack rides.  If I only had knobby tires, the speed difference would probably be even greater.
The Specialized Crux that you're considering seems like a pretty good choice.  It has 38mm tires out of the box, which is nice especially since you're used to mountain bike tires.  Tires of that size have a much less harsh ride than thinner tires (28mm), and don't slow you down (people used to think that, but research has shown that it's not the case).
Two things to consider about that bike: The brakes are cable/hydraulic hybrids; there is a brake cable that connects to a hydraulic piston.  I'm not sure if those are as good as regular hydraulic brakes; there is probably a bit of friction in the cable.  The other thing is the gearing: for hills you might want an 11-32T cassette instead of the 11-28T.  Depends on how strong you are and how steep the hills are.
If you care about riding in the winter, go to a Specialized dealer and ask if you can install fenders on that bike, and what size tires will work with fenders.  To attach fenders, you generally need eyelets (threaded holes in the frame). If the frame doesn't have any of those, it makes it very difficult to mount fenders.
Comment: I'm not sure if product recommendations are allowed here, but if there is a Norco dealer near you, check out the Threshold CX bike. Shimano hydraulic brakes, Ultegra components, Carbon frame, for $3325. http://www.norco.com/bikes/road/cyclocross/threshold-carbon/threshold-sl-ultegra/
Comment: Re fenders:  I have a road bike with no eyelets.  I have a rear fender that clamps to the seatpost and was told that I don't need a front because the downtube takes care of that, which makes sense to me.  As we are in a drought in California I can't say this is correct.
Comment: The rear fenders with the seatpost clamp are OK, but you still end up with a lot of dirt/mud being thrown at the seat tube and the front derailleur.  For the front wheel, the down tube doesn't work very well as a fender because as soon as the wheel is turned a bit, the water and dirt is directed at your feet and legs; also, the lower steering bearing will take a beating.  As you pointed out, depending on where you live, it may not matter that much.
Comment: @Nik Giving product recommendations in an answer is fine, as long as it's relevant to the question at hand. Just note that if you are affiliated with the product, you [must disclose that affiliation](http://bicycles.stackexchange.com/help/behavior). Asking for product recommendations is [off topic](http://bicycles.stackexchange.com/help/on-topic) because the answers tend to be [highly opinionated, often solicit spam](http://meta.bicycles.stackexchange.com/a/967/4239), and go out of date quickly.
Answer: The easiest way to tell is by going to a bike shop and test riding few bikes. I had the same decision to make recently (road or CX), and after test riding, I was confident I wanted to CX. The road bike was noticeably faster, but the comfort on the CX trumped that for me, and it was still very fast (33C road tires, compact gearing). It is also running without problems on trails and gravel(as its supposed to), which is a plus as I can take tours through the woods ( as long as the trails relatively flat, eg for hikers/hourses).
I think the main things to consider are: do you care for off-pavement rides?
Is the pavement quality good? if there are too many bumps, road bikes can be a pain, while the thicker CX tyres will help.
Finally, depending on what you prefer, you might want to ask to test ride road bikes with a relaxed geometry, that will again be more comfortable.
Answer: Also look at touring bikes.  Road and CX bikes are made for racing. Which means they have a quite aggressive fit which makes you lean over the handlebars quite a bit.  Touring bikes are much more laid back and comfortable, while still being very efficient. They have room for racks, fenders, and big tires which can be nice for riding in the city.  If the bike show you're dealing with focuses on the Specialized brand, then take a look at the Awol.  If you are happy with Trek, then look at the 520.


Magento 2 Component less/css editing best practices

Question: Please help to understand below 2:
1. How to override component css using less files?
2. Is anyone can provide some of examples to write css in _extend.less file.
Answer: You can add in your theme app/design/fronted/PackageTheme/YourTheme/Aheadworks/Autorelated/web/css, and copy the CSS file from app/code/Aheadworks/Autorelated/view/frontend/web/css, and there you can change it.
For edit in LESS file, you must add _module.less file in this path app/code/Aheadworks/Autorelated/view/frontend/web/css/source and you can also copy the CSS content from CSS files in _module.less and you can edit.
After that you must run php bin/magento setup:static-content:deploy

Best Practice:

You should not edit/modify files within pub/* or vendor/* directory. Pub is for deployment and vendor is for default structure, which you override via your template or custom modules. Instead:

create a new theme inside app/design/frontend/{vendor}/{yourTheme}/. You can use Blank or Luma theme. You can also create new theme which inherites from Blank (inheritance is defined within theme.xml). If you are already using some theme then skip this step.
edit .less within your theme so the changes stay visible and don't get replaced when clearing the cache or upgrading the system.
Use grunt to compile your .less into deployment files.
You can also setup sourcemaps to pin point your styling within the theme .less files so you can be more productive.

I hope this will help
Comment: My question is slightly different. Actually I am overriding the luma theme as per best practices as suggested in official docs. Trying to get further understanding on luma theme less file editing. For example if I need navigation css changes, what should be the best practices. Should I directly add the css or I need to change the mixin/variables codes. Just trying to best way of theme css editing.
Comment: @KamleshYaduwanshi I add more detail in the answer, hope this will help you and other readers
Comment: I am following all these best practices, just wants to know whether I edit the less codes mixing and variables or write regular css.


How to properly image a truecrypt system partition?

Question: A couple of times now I have imaged a truecrypt system partition in windows. When the system has crashed on me I've attempted to recover the system only for truecrypt to not boot the recovered system. Has anyone successfully backed-up and restored a system truecrypt partition?
Comment: Not while encrypted, no.
Comment: so then truecrypt essentially prevents anyone from imaging a drive and investigating it lively?
Comment: Effectively, yes. It also allows the partition within a partition which makes a good dummy if someone gets hold of the first password.
Answer: You can backup and restore a TrueCrypt system partition if you use imaging software that is capable of reading and writing in raw mode -- copying the whole partition byte for byte without regard to the underlying file system.  You also need to back up the MBR (master boot record), and perhaps the data between the MBR and the first partition.
And you must not image it when running Windows, like with "hot running" image software such as Acronis TrueImage. You must boot from a separate disc (CD or external drive) with your imaging software and then take the image.
I used Clonezilla to back up and restore a Linux encrypted root partition and MBR; I don't see why it shouldn't also work with a TrueCrypt encrypted partition.
Sometimes the problem is only with the header of the TrueCrypt partition, and restoring just the header might solve the problem.  TrueCrypt provides the ability to backup and restore the header (you'll need to boot with the TrueCrypt rescue disc or another Live CD to restore the header).
Which software did you use in your backup and restore attempts?  I would recommend Parted Magic, which is a Live CD that contains disk imaging and partitioning utilities (including Clonezilla), and also includes TrueCrypt.
Comment: I was able to get a truecrypted disk-to-disk copy working using Parted Magic.  The Clonezilla options I used were -e2, -j2, -ql and Use Partition Table.  Afterwards I had to use the Truecrypt rescue disc to restore both the boot loader AND key data.  It took over 15 (!) hours to clone a 160 GB drive.  I suspect that if I'd had a 500 GB drive, it would have been much, much faster to just reinstall Windows and all my software.
Comment: 15 hours for 160 GB is an unusually long time.  Were you cloning over the network?
Comment: Disk cloning of large encrypted drives is time consuming whether it is 2 hours or 15 hours, especially because the cloning software can't skip over the empty space.  What I do to minimize that is keep the system partition fairly small like 20GB, then use a huge separate partition (also encrypted) for everything else.  So when I have to clone/restore after a crash, it's just 20GB and I'm up and running in an 1 hour. If I'm lucky the extra big partition is still accessible without any rescue operation necessary, otherwise I can just copy back the files from an external backup drive.
Comment: I just used Clonezilla and it worked just fine and very fast. Between two SSDs, I got >11GB/s. I used the expert mode but used the default choices, and my new SSD booted just fine. The only thing I need to do now is to expand the partition on the new disk.
Answer: I have had many successes at cloning TrueCrypt encrypted system volumes.  If you clone outside of Windows and make an exact clone (cloning MBR, partition table, and partitions WITHOUT any resizing or re-arranging of partitions) all should work as expected.
That said, I've also had one (repeated) failure which I was wasn't able to explain.  Maybe it was the software I was using that time versus the software I used in on the other occasions (I failed to clone with Acronis Disk Director, latest version as of 8/15/2012, I don't recall which software I was successful with).


How much data (MB) does Skype consume in a 1 minute call?

Question: How much data (in megabytes) does Skype consume in a 1 minute audio call? And how much data does Skype consume in a 1 minute video call? Is it fixed or does it vary with the mobile version or PC version of Skype?
Comment: How to test it?
Comment: Why not test it?
Answer: As Gaurav Joseph has said you can monitor this through the resource monitor or using another network monitoring tool to obtain your usage.
As an approximate guide Skype says the following are examples of typical data usage.

Skype-to-Skype calls: 50kbps or around 375KB for one minute of calling
Calls to mobile numbers or landlines: 6-20 kbps or around 150KB for one minute of calling
Video calls between two mobile phone devices: 500kbps
Video calls between a mobile phone and a computer: 600kbps

How much data will Skype use on my mobile phone?
If you take these figures you are looking at approximately 3.75 MB for a video call between two mobile devices for 1 minute.
Skype also recommends different bandwidth requirements for different situations.
How much bandwidth does Skype need?
HD video calling has a recommended upload and download speed of 1.5Mbps both ways so you are looking at about 22.5 MB per minute.
To answer your last question as Skype is a peer to peer application and will try to make the best use of the bandwidth it has available so the rate is variable and not fixed.
Answer: You can also use sysinternals process explorer to monitor skype.exe. In "disk and network" tab it shows you exact speed and number of bytes transfered over network.
Answer: You can use the resource monitor to check it out in windows. The data may vary on versions of skype due to compression algorithms and other factors.


What do the different coloured dots mean?

Question: While playing Fire Emblem, I noticed that there are places on the map that are different coloured dots. There are red and green and purple ones, along with the more normal white ones. What is the meaning of the different colours?
Comment: I THINK those correspond to what you can buy, but not 100% on that.
Answer: There are a few different colors on the map.  @gorogoro got most of it right.

White dots are completed story maps, and allow you to buy items from them, as long as a random encounter isn't there.  If a Merchant is there, the selection is expanded the first time you shop there, with an item or two being on sale.  The discount depends on the item (ie. Master Seals only get 9%, while Iron weapons can get close to 20%).  You can also encounter random Risen battles here, and their difficulty is directly relative to what the story levels were.  ie. A random encounter at Ylisse will be significantly easier than one encountered at Ferox Arena, or further in the story.  If you fight a random battle at a spot that has both a Merchant and a Risen, the Merchant will be on the map.  Saving them grants you a free random item.
Red dots are the next story mission.  There should only be one of these available at a time (unless the path splits, and I haven't reached that yet).
The single purple dot is the DLC spot.
Green dots are the Paralogue mission.  These are extra, optional missions that you can choose to undertake, and get unlocked at certain points in the story.  Essentially side quests.  Some will reward you with extra characters (Paralogue 1 & 4), while some just expand the story, and provide extra experience and items.
Orange dots are maps gained from SpotPass.  These are added to specific areas on the map, and you have to be far enough in the story to challenge them.  You can unlock them before you can challenge them, and they will sit there until you get far enough in the story.  They seem to be extra missions, just like Paralogue ones, so they might reward you with the same things.
Comment: The map will also show a small red/purple face where random Risen battles can be fought.
Answer:
White dots: Main story battles that you have completed
Red dots: The
next stop in the main story.
Green dots: A series of maps that can
only be unlocked after completing certain chapters (I don't know if
I can explain more because it's quite spoilerific, but you can
access the first one after Chapter 13). Streetpass maps also uses
the green dots. You can recruit extra units in these maps.
Purple dots: Random Risen battles where you will get bullions for clearing
them (it appears randomly from time to time).
There is also the
orange dot which are bonus maps you can get via Spotpass, you can
only access them after you have completed the 2nd last chapter
though.
Comment: I have seen the green dots before chapter 13.


What is the physical meaning of a primary field?

Question: In the book Conformal Field Theory (authors: Philippe Di Francesco, Pierre Mathieu, David Senechal), a field $f(z)$ is primary if it transforms as $$f(z) \rightarrow g(\omega)=\left( \frac{d\omega}{dz}\right)^{-h}f(z)$$ under an infinitesimal conformal transformation $z \rightarrow \omega(z)$. The physical meaning of this definition is unclear to me. For instance, what's the difference between a primary field and a secondary field? And what's the significance of the fact that the energy-momentum tensor is not a primary field?
Comment: What do you mean by the "physical meaning"? Fields are **not** observables. However, being a primary field reflect in transformations property which in turn appear in the operator product expansions and in the expectation values.
Comment: For example, why we call the term in the OPE of $TT$ which should not appear if $T$ is a primary field a anomalous term? anomalous for what, just for the transformation?
Comment: The term anomaly is related to the fact that the Virasoro algebra can be related to extension of the de Witt algebra plus a central term (not entirely sure though, however that should be where the terminology comes from).
Comment: Minor comment to the post (v2): Please consider to mention explicitly author, title, etc. of link, so it is possible to reconstruct link in case of link rot.
Answer: In fact, primary fields(operators) sometimes are also called tensor field(operators). The name is justified as they transform in the same way that a tensor transforms under coordinate transformation.
To see that, we look at the transformation rule of primary fields, which by their definition, is $$\mathcal{O}'(z',\bar{z}')=(\partial_z z')^{-h}(\partial_{\bar{z}}\bar{z}')^{-\bar{h}}\mathcal{O}(z,\bar{z}).$$ Compare that to the transformation rules of a tensor with $n$ lower indices. $$T_{u_1u_2\dots u_n}'=\frac{\partial x^{v_1}}{\partial x'^{u_1} }\frac{\partial x^{v_2}}{\partial x'^{u_2}}\dots\frac{\partial x^{v_n}}{\partial x'^{u_n} }T_{v_1v_2\dots v_n}.$$ Note in the case of 2d conformal transformation, in terms of $z,\bar{z}$ coordinates, $z'$ is only a function of $z$. Thus $\frac{\partial x^{v_i}}{\partial x'^{u_i}}$ is non zero only when $v_i=u_i$. In other words, various $\frac{\partial x^{v_i}}{\partial x^{u_i}}$ are either $\frac{\partial z}{\partial z'}$ or $\frac{\partial \bar{z}}{\partial \bar{z}'}$. Therefore we can write $\frac{\partial x^{v_1}}{\partial x'^{u_1} }\frac{\partial x^{v_2}}{\partial x'^{u_2}}\dots\frac{\partial x^{v_n}}{\partial x'^{u_n} }$ as $(\frac{\partial z}{\partial z'})^h(\frac{\partial \bar{z}}{\partial \bar{z}'})^{\bar{h}}$, or with $(\frac{\partial z'}{\partial z})^{-h}(\frac{\partial \bar{z}'}{\partial \bar{z}})^{-\bar{h}}$ with $h+\bar{h}=n$.
Thus we just demonstrate that $\mathcal{O}(z,\bar{z})$ obeys the same transformation rule as a (component of a) tensor, and thus it is called a tensor field.
Finally, the direct consequence of $T_{zz}$ not being a primary field is that it does not transform as a tensor. Moreover because it does not transform as a tensor, its OPE can have a $z^{-4}$ term, which is related to the Casimir energy for a unitary CFT.
Comment: Well, you're just rephrasing the question as "the stress energy tensor not being a primary field means it doesn't transform as a primary field".
Comment: Your answer is correct as long as we are looking at classical CFT's. When we are considering a quantum CFT, then the classical dimensions acquire anomalous dimensions, and hence tensor algebra cannot account for that,as  it will only give is integer powers. Hence, your answer is true but only classically.


Is there a way to get convexity adjustements for any CMS-payoffs?

Question: In the litterature we specify a dynamic for $\frac{P(T,T_{p})}{A(T)} = G(S(T))$ for each Swap rate S(T) , and there are supposed independant so that we can obtain some value using copulas for calculing the CMS spread with payoff $( S_{1}(T)-S_{2}(T) - K)_{+}$.
But in reality the swap rates are not independant so that we cant'suppose the same G(S(.)).How do we account for this ? Is there a way to model those " annuity mapping function" consistent with swaps rates dependance?
Answer: To the extent that I understood your question:

You want to capture the marginals of the 2 rates perfectly, since they will be your hedging instruments. You can correlate them with a copula.

You need to model a change of measure from the annuity to the T-forward measure. This can be done in a simple hull white setting.

Pricing is then trivial.
Let me know if I misunderstood the question.
Comment: Yes , that's pretty much it ,The distribution of $S_{1}(T)$ and $S_{2}(T)$ in their annuity measures can be mapped into the distribution under the $T_{p}$ forward measure using standard techniques like the copula method. The problem is not the copula method itself but rather the meaning of the parameters for the dependance structure. It should reflect both the correlation of rates observed at the same time and their inter temporal de-correlation.\\
What should i chose to account for this in the change of measure , which model better suits for this ? Libor Market model , hull white setting ?
Comment: How would the copula method help in modeling the change of measure? Can you describe it? What you need to model is the annuity (or possibly bond/annuity) as a function of the swap rate. You can do this in a HW setting. This is sufficient to get the distribution to the Tp measure. The copula is to only correlate both the underlyings (i.e go from marginal distributions in the Tp measure to the joint).
Comment: Ok thank you a lot , and if i have two different fixing dates is it the same thing ? or the distribution to the T-p measure will be modified ?
Comment: Interesting. If you have significantly different fixing dates then the copula approach would not really go through. You will have to make assumptions about the delay effect in some way. You can still price in the Tp measure, but keep in mind that your product is starting to become more and more like a forward starting swaption, so you will nees stochastic vol if delay is significant.
Comment: Consider accepting the answer if I did answer your question.


Recommended way to embed Google Drive inside a WebView?

Question: I have embedded a Google Drive webpage inside a webView in Mac OS X, but in this case the webpage is not fully functional:

It's not possible to Drag & Drop a file from the filesystem inside a document, (while it's possible to drop an image from another application)
The "Share" button does not work
The Print Button does not work
Multiple entries for the same user appear into the chat when opening the same document various times. The expected behavior is that the number of entries decrease when the user close the page.  When a document is shown inside a Mac OS X WebView, the number of entries is increased correctly when opening a page, but it do not decrease when the WebView is closed.

I want to understand what is the recommended way to embed a Google Drive page inside a WebView to avoid all these issues.

Additionals information:

WebView documentation
All the requests are authenticated using the Google Drive Oauth access token.
Answer: There is no current recommended way of doing this, it should just work as if you are viewing Google Drive in any browser. Authorization should be done by the cookie though, Oauth token won't help you here.


Lightning Filter Component

Question: We are building a component that allow user to search for list of records. Was wondering if there is a standard filter component that can be applied with the possibility to apply multiple fields and filter logic (similar to one we use on listviews).
Comment: Do you want the user to be able to create and define filters or would this be controlled by configuration / developer?
Answer: There is no Out of the box compnent that will meet your requirement - you will have to create your Own custom component + filter component or use an appexchange managed package that offers the functionality you are  looking for.

Lightning Filter Component


Is it possible to hide the title bar or to combine it with the menu bar and/or toolbar

Question: Is it possible to hide the title bar in TexStudio, or to combine it with the menu (and/or tool) bar? I want to do this to save up space as my laptop screen is not that big. I researched it online and looked trough the settings but by the looks of it, it does not appear to be possible.
Comment: someone knows how to do the same move on overleaf?
Answer: In order to hide the title bar, you can use the built-in full screen mode by pressing F11 or by going to View > Full Screen. However, only hiding the title bar might not make such a big difference. Maybe it is more beneficial to hide toolbars and other panels (e.g. the side panel), because TeXStudio has quite a lot of them and most functionalities are already easily accessible via hotkeys or the menu bar.
Comment: As this does hide the ttitle bar, it also hides the taskbar. I was more thinking about what firefox and microsoft office do for example. In this case that would entail replacing the path name that is displayed, by the menu bar and possible other bars.
In terms of creating space, I already disabled most of the toolbars and in normal usage I either view or hide the PDF example over the full width.


VS 2015: Selenium webdriver reference isn't found

Question: I just started with Selenium and C# and came across this problem at very beginning. I've installed nuget webdriver package in project WebdriverTest, then created Unit test project in which I add reference to WebdriverTest project.
But the unit test doesn't recognize the selenium webdriver reference in WebdriverTest project at all.
Comment: This is actually a basic coding question. If you want to use WebDriver in your UnitTest Project, you must have the WebDriver reference in your UnitTest project, not just the other project in your solution.
Answer: The project reference for "WebdirverTest" in the UnitTest project's references does not include any libraries that are in "WebdirverTest", it only includes references to classes within that project. You must add the library to both projects. As @ChathuD said, the Nuget Package Manager is a useful tool for doing so.
Answer: Try Nuget manager or use Package Manager Console with below command:
Install-Package Selenium.WebDriver -Version 2.53.1


splitting files for P2P application

Question: I have to implement a middleware system for file sharing, and it has to split the files not unlike what happens on bittorrent, where it sends and receives separate pieces simultaneously from varios sources. How do i do that? Is it a library or i have to implement the file splitting myself?
Answer: Split the files into blocks let's say of 100KB each.  Then calculate a SHA hash (or some other hashing algorithm) on each of the blocks.  so if the file is 905KB, you would have 10  such hashes calculated.
The server would contain a hash definition file for each file that it serves.  This hash definition file would contain a list of all of the blocks of the file, along with the hash.   So if the server is serving our 905KB file called test.exe.  Then we would have another file called test.exe.hashes which contains a listing of the 10 hashes of the file.
The client would download the hash definition file, and ensure that it has all of the blocks.  The client can request each block individually and after it's downloaded, it can calculate the hash on its end again to ensure there is no corruption.
You don't need to physically split the file, splitting a file is just reading the part of it that you are interested in.  The first block of the file is from byte range 0 to 102399, the next block is from 102400 to 204800, and so on.  So just open the file, seek to that position, read the data, and close the file.
Answer: Look at the implementation of Split & Concat (GNU software).
Answer: You might want to consider using Solomon-Reed encoding.  It will make getting the final blocks much easier.  This is the route Microsoft took in Avalaunch.
Answer: Out of interest: Why not just implement BitTorrent or something like that? There are many OpenSource Clients (i.e. Azureus) and the protocol is really simple. There is also an article with a little more detail, but this contains some extensions - in doubt, the official spec is always right.

splitting files for P2P application


What is tissue gel?

Question: My book consists of following lines."The interstitial fluid is entrapped in minute space among proteoglycan filaments. This combination of proteoglycan filaments and the fluid entrapped within them has a characteristic of gel so called tissue gel.  Instead of flowing interstitial fluid mainly diffuses through gel.  This diffuion allows rapid transport of interstitium of water nutrients,oxygen,cell excreta e.t.c.
I can't get the meaning of these lines.  I tried to search on net but didn't get a satisfactory explanation.  Please explain this to me.
Answer: In the question, "tissue gel" clearly refers to "proteoglycan filaments and the fluid entrapped within them" and which appears in the interstitial space.
This is the same as what the Wikipedia article says about Extracellular matrix:

Gels of polysaccharides and fibrous proteins fill the interstitial space and act as a compression buffer against the stress placed on the
  ECM. (Source: Essential cell biology, 2004)

A.C, Guyton et al from University of Mississippi School of Medicine, 1973 also says the same:

Though 1/6 of most tissues is composed of interstitial fluid, this
  fluid is generally held tightly in place in the form of a gel. The
  reticulum of this gel is composed mainly of hyaluronic acid, but this
  is cross-linked slightly with collagen fibers to form a meshwork in
  which the interstitial fluids are trapped. The presence of this gel
  reduces the mobility of fluid in the tissues...

The exact term "tissue gel" is very rarely used in biology or histology, though.
You are probably confused because of this sentence, which is messed up: "This diffusion allows rapid transport of interstitium of water, nutrients, oxygen, cell excreta e.t.c. " It should be: "This diffusion allows rapid transport of water nutrients, oxygen, cell excreta e.t.c. through the interstitium."

What is tissue gel?


Quickblox frequent crash in Android

Question: I have been working with Quickblox SDK for past few weeks and have developed applications with features of one-to-one, group chat as well as WebRTC too.
I am using 3.0 version of the SDK due to some of my requirements and I will not be able to change it.
There is one crash which I am frequently facing in my app in no specific screen. I have reported this to Quickblox as well but did not help much.
The crash log is as below :
<code>java.lang.NullPointerException:
at com.quickblox.chat.model.QBChatDialog.initChat (Unknown Source)
at com.quickblox.chat.model.QBChatDialog.initChatFromRest (Unknown Source)
at com.quickblox.chat.model.QBDialogDeserializer.deserialize (Unknown Source)
at com.quickblox.chat.model.QBDialogDeserializer.deserialize (Unknown Source)
at com.google.a.v.b (Unknown Source)
at com.google.a.b.a.l.b (Unknown Source)
at com.google.a.b.a.b$a.a (Unknown Source)
at com.google.a.b.a.b$a.b (Unknown Source)
at com.google.a.b.a.i$1.a (Unknown Source)
at com.google.a.b.a.i$a.b (Unknown Source)
at com.google.a.f.a (Unknown Source)
at com.google.a.f.a (Unknown Source)
at com.google.a.f.a (Unknown Source)
at com.quickblox.core.parser.QBJsonParser.parseJsonResponse (Unknown Source)
at com.quickblox.core.parser.QBLimitedJsonParser.parseJsonResponse (Unknown Source)
at com.quickblox.core.parser.QBJsonParser.parse (Unknown Source)
at com.quickblox.core.Query$a.completedWithResponse (Unknown Source)
at com.quickblox.core.Query.completedWithResponse (Unknown Source)
at com.quickblox.core.server.HttpRequestRunnable$1.handleMessage (Unknown Source)
at android.os.Handler.dispatchMessage (Handler.java:111)
at android.os.Looper.loop (Looper.java:238)
at android.app.ActivityThread.main (ActivityThread.java:6006)
at java.lang.reflect.Method.invoke (Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:937)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:798)
</code>
Just to be noted, I could not find any file with method using any of mentioned in crash log like initChat() or anything else and crash can come to any of the screen in app. So not sure which code I should share here.
I would be thankful for any suggetions.
Comment: please answer me, did you test my recommendation below, what is result?
Answer: Looks like you load dialogs and not logged in to the chat in this moment. Use latest version of QuickBlox Android SDK with fix this issue.

Quickblox frequent crash in Android


Asp.net MVC routing ambiguous, two paths for same page

Question: I'm trying out ASP.NET MVC routing and have of course stumbled across a problem. I have a section, /Admin/Pages/, and this is also accessible through /Pages/, which it shouldn't. What could I be missing?
The routing code in global.asax:
<code>public static void RegisterRoutes(RouteCollection routes)
{
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
        routes.MapRoute(
            "Pages",    // Route name
            "Admin/Pages/{action}/{id}",  // URL with parameters
            // Parameter defaults
            new { controller = "Pages", action = "Index", id = "" }
        );

        routes.MapRoute(
            "Default",   // Route name
            "{controller}/{action}/{id}",   // URL with parameters
             // Parameter defaults
            new { controller = "Home", action = "Index", id = "" }
        );

    }
</code>
Thanks!
Answer: I'd suggest adding an explicit route for /Pages/ at the beginning.
The problem is that it's being handled by the Default route and deriving:
controller = "Pages"
action = "Index"
id = ""
which are exactly the same as the parameters for your Admin route.
Answer: For routing issues like this, you should try out my Route Debugger assembly (use only in testing). It can help figure out these types of issues.
P.S. If you're trying to secure the Pages controller, make sure to use the [Authorize] attribute. Don't just rely on URL authorization.
Comment: This should be the answer because the intent is to secure the Index action method of the PagesController.
Answer: You could add a constraint to the default rule so that the {Controller} tag cannot be "Pages".
Answer: You have in you first route {action} token/parameter which gets in conflict with setting of default action. Try changing parameter name in your route, or remove default action name.


Can heat be collected and concentrated?

Question: If a pipe that is 1km long can collect low grade heat that may raise the collecting liquid by 5 degrees. Is there a device that will concentrate that into a heat exchanger that is 1m long at say 50-90 degrees so the distance and change in temperature balances.
This is to increase the low grade heat from a ground or air source to medium grade heat suitable to warm a home (which has far less volume than the ground that the heat was extracted from) to a comfortable level (many heat pumps have a COP of 4 or above but the heat generated gets lost too fast to warm a home properly).
Note: how does a heat pipe freeze the ground or keep a permafrost without the use of electricity? And how does a room have a higher temperature at the ceiling than the floor?
Comment: Maybe the laws of thermodynamics help a bit. Zeroth law: you must play the game. First law: you cannot win. Second law: you cannot tie. Third law: you always lose. The rest is details.
Comment: I've heard a similar quip regarding the laws of thermodynamics.  You can't win, you can't break even, and you can't get out of the game.
Comment: If you have a really hot system a long way away and a parabolic mirror, you get to cheat.
Answer: Heat moves spontaneously from hot systems to cold systems. This is the definition of temperature.
A device which moves heat from a cold system to a hot system is called a "refrigerator."  (If the point of the refrigerator is to increase the temperature of the hot system, it is sometimes called a "heat pump.") A refrigerator, even an ideal refrigerator, requires external work input which depends on the temperature difference between the two systems.
Comment: You say tomato, I say [technically a berry](https://en.wikipedia.org/wiki/Berry_(botany)). "Refrigerator" has the pedagogical advantage that people who have not yet studied thermodynamics already know exactly what the device does. The phrase "heat pump" tends to startle the novice: surely it can't mean what it sounds like it means, because what would it mean to pump heat, like some kind of a fluid? That's an hour's worth of introductory thermo that I'd rather not clutter this brief answer. For you, @SolomonSlow, that hour happens to be in your past.
Comment: IMO, you're reversing the roles of those two terms. "Heat pump" is the generic term, and "refrigerator" names a specific application of a heat pump.
Answer: It doesn't matter how you try, unfortunately there is no way to make heat flow from an area of lower temperature to an area of higher temperature without energy input. One of the side effects of this is that you can't collect heat energy from the ground at say 60 degrees F and have it flow into a home at 70 degrees F. Doing so must require energy. This is the same reason that if you focus light from the sun using a huge magnifying glass you can never achieve a higher temperature than the sun.
Because of the 2nd law of thermodynamics, energy always wants to spread out. There is no way to make the energy from the 1km long pipe concentrate itself together in a 1m long pipe without using energy (like a heat pump) to do so.
You are right that in both cases the total energy might be the same (5 degree 1km long pipe vs. 90 degree in 1m long pipe), but the useful energy isn't the same in both cases.
Comment: How does a heat pipe move heat from a hot processor to a cooling fin then? With no moving parts or fans! And no use of electricity?
Comment: @Lonewolf Heat pipes use a liquid inside: it evaporates at the hot end and condenses at the cooler end. Like those drinking bird toys.
Comment: So could these be used to concentrate heat over time?

Can heat be collected and concentrated?


arcserve brightstor 11 next tape email

Question: Is there anyway of getting brightstor 11 to email out to a group of users when a new tape is required for a backup job (ie when the backup on a particular day spans over multiple tapes). At the moment we have to physically visit the server or rdp to it and check to see if the screen pop has come up.
Answer: CA ARCserve r11 is no longer a supported version of ARCserve Backup. CA currently has version r15 out and are almost at version r16.
Reporting and alearts have been greatly enhanced in the latest version with a Dashboard feature that has 38 reports and email alearts.
For version r11, it might be useful to check the guide for alearts. Let me know if you need help finding it.

arcserve brightstor 11 next tape email


Adding additonal NIC on guest VM - linux KVM

Question: How to add additional NIC to guest VM machine, on linux KVM using virt-manager
Comment: if you dont have any way to alter the vm, maybe you're in virt-viewer?
Answer: in vitr-manager open the guest window and on topbar is lightbulb icon. In this window you can add hardware.
Some hardware can be added only vhen guest is poweroff or need restart after change
Answer: I am not sure this question is a great fit for SF, in part because I am not sure the situation you describe fits within the topics you can ask about here.
It isn't clear from your question if you have the required rights to do what you are trying to do - are you the VM administrator, and are you able to configure/modify any parts of the setup?
You may find some use in looking into virsh, notably its iface-* operations.
Alternatively, if you are comfortable with vi and XML, you can virsh edit your guest to add a NIC.
The fact you have no options to edit your guest via virt-manager would however suggest you may not have enough access/rights to do what you are trying to do.
Comment: I have **root** access and i want to add additional NIC to configure **teaming**, but i am unable to find any option on **virt-manager**, even when the guest is **power-off** there is no option to edit the config
Answer: If you use Cloudstack, you can do this easily.
Cloudstack has option to choose particular bridge for guest traffic.
If you are not using Cloudstack, create another bridge with new nic and edit the xml file directly and replace the existing bridge in configuration file with new bridge.
Answer: I found options in the guest panel under view options console and details where i can edit details in details option
Comment: If this question is solved, please mark it as solved by ticking the check mark next to the answer. Thank you!


Is the Fischer Esterification mechanism very simplified?

Question: Example mechanism:

Is that very simplified, or is that pretty much what is very likely happening at the molecular/atomic level when you do the reaction in real life?  (Of course besides the free $\ce{H+}$, that is obviously hydronium, protonated alcohols, or the acid itself.)
Comment: You can write 8 mechanisms for both esterification and deesterification. As long as the mechanism is reasonable, it has a right to live.
Answer: That is the wrong question to ask. Mechanisms are putative pathways. Accepted mechanisms are mechanisms that we have not found evidence to refute. There is no way to determine whether a mechanism is the true mechanism.
Comment: This isn't exactly actual. There are methods that let analyse mechanisms directly.
Comment: You have a window but that doesn't rule out things that you aren't measuring. Your putative mechanism is consistent perhaps but not _guaranteed_ to be correct. @Mithoron
Answer: What Zhe has said is undoubtedly correct.
However, the currently accepted mechanism that is taught in lectures typically represents exactly our understanding of how a mechanism would work. There may be non-productive side steps, there may be backwards and forwards shuffling, but the effective pathway that a molecule takes will — under the assumption that the mechanism is correct at all — happen in pretty much exactly that order.


why are tau-jets narrower compared to quark-jets?

Question: I read in a thesis (no online link provided) that tau-jets result in a narrower cone in comparison with the other quark/gluon originated jets. I don't understand this. Is this true? If so, why?
Comment: The ratio of mass and transverse momentum apart fromthe R parameter and the clustering algorithm of choice will define the shape of the jet.
Answer: The tau decay hadronically thorugh neutrino + Wboson (greater Branching ration). And then the W boson decay in one charged hadron (narrow jets).
In QCD things are a little different, gluons/quarks for example doesn't have neutrino on his decays and then multiplicity on final state is larger, more hadrons produced (wider jets).
And gluons can produce more jets than light quark jets (higher multiplicity), gluons jets are wider than quarks jets.
Comment: Do you know if all jets need a hadron to be defined? Are there non-hadronic jets (in particle physics)?


Switch workspaces individually on each monitor

Question: In 12.04 with a two monitor setup (using unity and compiz), is it possible to switch workspaces individually for each monitor?
Answer: I spent considerable time trying to find a solution for this. My conclusion is that while compiz once had support for this, it has not been functional in a while. Since Unity uses compiz, it cannot do it either at the moment.
There seem to be very few window managers that support this feature at all. The only one I was able to find was xmonad, which is a keyboard-driven tiling window manager intended for power users willing to spend quite a bit of time learning how to use it. I think I've seen references to awesome being able to do this too, which is another similar tiling window manager.
So unfortunately the answer for compiz and unity seems to be "no, not possible", and the answer more generally seems to be "no, not unless you are willing to switch to a tiling window manager".
Comment: Awesome does that, but it does that only. If I understand correctly, each monitor has its own set of workspaces and you cannot show a workspace of monitor 1 on monitor 2. Maybe it's configurable, but I've read several people complaining about that. That drove me away from Awesome.
Comment: You can easily move a window to the other monitor (Mod4 + o), so it's also pretty fast to have the whole workspace (i. e. every window) moved over to the other screen.
Comment: Is this still true for 15.10?
Answer: I know this is old, but for people looking into this, Enlightenment 0.19.x (http://enlightenment.org) has good support for multiple screens, and is able to switch workspaces independently or simultaneously on two screens (haven't tried with three or more). I switched from xfce4 and haven't looked back. You can find a PPA at https://launchpad.net/~niko2040/+archive/ubuntu/e19
EDIT: The reason this isn't common functionality is that it violates a freedesktop.org specification (EWMH - http://standards.freedesktop.org/wm-spec/wm-spec-latest.html) that most window managers follow. Those window managers that support this simply do not follow the specification.
Comment: your explanation of the reason this isn't common functionality is certainly useful, but it leaves me wondering why the spec doesn't cover this use case. I'm also wondering if that spec has any relevance when it comes to Wayland compositors. I'm sure that's a separate question, however.
Comment: Then the spec is idiotic. Why, on earth wouldn't you want to move workspaces independently? Absolutely dumb.
Answer: Actually, you don't need to use a tiling window manager. As far as I know, xmonad and awesome support this feature, and i3 does to a certain extent.
But they are all tiling. Wingo is a hybrid window manager that has per-monitor workspaces, and it can be used as either a regular window manager or a tiling manager (or both). Note that it is self-described as "very alpha".
Comment: @BenjaminR That's false. Wingo is simply feature complete and will continue to work so long as I use it. (As the README says.)
Comment: awesome seems to *kind of* support this feature, but every monitor has its own set of tags (ie workspaces). The monitors are so separated that if you populate your workspace 2 with windows on monitor 1, you can't later show the content of workspace 2 on monitor 2.
Comment: i3 certainly supports this, it can also treat windows as "floating" (ie the way most window managers handles them). The floating property can be toggled on already opened windows or you can configure classes of windows to always open as floating. This may be handy for those who don't want to use tiling for all windows. Also, most dialogs automatically open as floating.
Comment: It's a shame development on Wingo isn't continuing, it's an interesting idea.
Comment: @BurntSushi5 Ah, good. Thanks for the clarification.


Losing my city on a one-city-challenge on complete kills, do I still stand a chance?

Question: I am currently in a long term Civilization game with a few of my friends. During our previous session I was one single turn away from a science victory, however, the warmonger among us managed to destroy my only city (due to one-city-challenge being on) with his superior fleet. Luckily for me, complete kills is also on, and I still have a decent army. Is it possible for me to capture a landlocked city-state, construct the final piece of the spaceship, and win the game?
Comment: Even if you manage to capture the city-state, it's going to be a LOT worse than your original capital city, so that final spaceship piece is going to take a while to build, and you'll still have to defend your other pieces. and if you already added those pieces, I think you even need to start building from scratch again.
Comment: I agree with your comments @Nzall, and worry for how i might deal with this. The other players seem to be completely convinced that i am out of the competition, so i will likely rely on underplaying my presence and flying under the radar, but it is still quite a challenge. I suppose we will see when we gather for our next session. I will post here again with a few answers when that happens.
Comment: And finally we managed to finish the game. As it turns out @Nzall my plan did NOT work. I got around the problem of poorly developed city-states as i already had adopted all tradition policies in addition to "Spaceflight Pioneers" thus allowing me to purchase a great engineer with saved up faith and use him to finish the spaceship part. However, this did not work because, even though i had no city, entering another city does not capture it, it simply removes it just like it otherwise would on one-city-challenge. The game-mode seams to refer to one city overall, rather than one city at a time.
Answer: It seams the answer is NO. One-city-challenge likely refers to one city overall and not one city at a time. In "Brave New World", capturing a city on one-city-challenge seams to remove it regardless to weather your original capital still exists or not.


Removing a data.stackexchange.com query from cache

Question: I noticed that a query on the stackoverflow data is cached after first execution. This is quite good, but how to force a re-execution? Since the underlaying data changed the query results are no more consistent with the present situation.
Answer: The data on data.stackexchange.com is "cached"; the data sets are updated once every week. Queries are not done against the live SE databases. See the data.se.com FAQ:

How frequently is Stack Exchange Data Explorer updated?
The data is updated early every Sunday morning around 3:00 UTC.

Query results are cached until the next dataset update, as the result of any one query and parameter combination is not going to change until then anyway.
Comment: Is it monthly or weekly?
Comment: These days it's weekly. When this answer was posted it was monthly.
Comment: there is an [AutoExpireCacheMinutes](https://github.com/StackExchange/StackExchange.DataExplorer/search?utf8=%E2%9C%93&q=AutoExpireCacheMinutes&type=) but I'm not sure what its setting is for production. I have doubts though if it allows for up to a week to be stored. My experience is that it isn't.
Comment: @rene: I run a set of queries weekly. Sometimes the weekly data dump process fails and I know it has failed because my queries are run instantly (== cache results are returned). The caches are cleared with the new data dump transfer being successful.
Comment: @MartijnPieters interesting, I would have to pay attention to this then. Unfortunately I don;t have access to the settings table
Comment: I have a query that returns 9-day-old data... maybe this changed
Comment: @xjcl: nope, it hasn't changed but sometimes the process fails.
Answer: While it's true that the general problem is that the data simply isn't live, the results of executing a query with a particular set of parameters absolutely are cached, and there isn't any way that normal users can purge them.
This can have some impact on the apparent correctness of the results if you use something in your query that's based on the current time, since after the first execution the selected reference point is locked in until that cache is cleared.
Since the data is only updated every month or so, though, it typically doesn't make sense to use the current time in your query at a granularity where it would be noticed anyway (i.e. the current day or hour). As such, the visible impact of the cache is quite insignificant*.
Currently, the cache will persist from the time that query is first run to the time that the cache is cleared manually. This manual purge is part of the process which updates the site statistics on the front page of the site, so you can be guaranteed that the cache will be cleared every time the underlying data is updated.
* However, if someone feels that there are cases where this isn't true, feel free to provide examples and I'll take a look
Answer: Data.SE is loaded with database dumps every month--it's not a cache you're encountering, and the data on data.SE is not updated live.
The last time it was updated was about a week back, so you probably need to wait ~three weeks for the next update.
Comment: Data has been updated monthly of late. The faq also reflects this.


How to determine which combinations of parameters to include in GridSearchCV

Question: I am using MLPClassifier from sklearn and I would like to tune it with GridSearchCV. But I don't know which set of values to include for hidden_layer_sizes, max_iter, activation, solver, etc. How can I determine the best combination to use in order to pass it to param_grid in GridSearchCV. How can I determine it?
Answer: There is no go-to when it comes to hyperparameter selection for the GridSearchCV since each problem/dataset is different and GridSearchCV will be the one to decide which one/set of params is the best. Opting for a exhaustive search to try out all the parameter combinations are resource consuming and simply not a good practice.
I believe that you are trying to figure out which set of hyperparameter values will be best suited for your MLPClassifier, Generally you don't have to worry about selecting any specific hyperparameters to begin with but there are few things you can consider while doing so.
1. Pick arbitrary values:
Be cautious when using random values since it might not work all the time but try to have a range from which you want the hyperparams to be from.
Try to include values with a fixed interval lets say 2,5 10 or even 100. That's why most data scientists pick arbitrary value ends with a fixed intervals as their hyperparameter candidates which is a far better approach than including all values from 1 to 100 (just as an example).
2. Understanding different hyperparameters and cross-reference from others:
A good understanding about the hyperparams will be crucial in-order to help you include only the required parameters without trying out everything which can save some time.
For example, for solver you can use 'Sgd' or 'Adam' to begin with since they are one of the most used parameters and Adam is a go-to for most people including me (You can also read some research work to see how others does it as well on projects that are similar to yours).
Similarly for params like max-iter (Maximum number of iterations), it is not optimal to include values that are too high, Let's say your arbitrary choice was 50,000 (would result in 50,000 epochs). So it is important to have some clue about each param you want to include so you can avoid obvious traps and mishaps.
3. Computational Constraints:
Try to assess what system/devices you are working with because you don't want to punish your setup by entering extremely high values for params like max-iter, hidden layers etc.
It is generally a good practice to not have very low or very high values for certain params like max_iter and hidden_layer_sizes since low values may result in poor performance and extremely high values might put unnecessary computational stress on your device.
These above measures can indeed help you solve your problems when it comes to selecting hyperparams for grid search.
You can also read the Official documentation for more details on what each hyperparameter does and on how you should approach them.


Prerequirements to start with JDBC

Question: I am new to JDBC. I would like to know what I should install in my machine before starting off with JDBC. It would be most appreciated if you can also give me links to find them.
Answer: read the tutorial first.
http://download.oracle.com/javase/tutorial/jdbc/index.html
Answer: Besides a working database, all you need is the JDK and the database-specific JDBC driver. You'll need to find and download the driver for the database you're going to use.
If you want to learn JDBC and don't care about a specific database, I can recommend HSQLDB, which is a lightweight DB that you can run on your machine or even from your process.
And I agree with qrtt1's advice - the best place to start is Sun/Oracle's JDBC tutorial.
Answer: Read "Before you Begin" in this JDBC Tutorial; for use with any JDBC Database, including Oracle, PostgreSQL, MySQL, etc.
Pretty much all you need is:

JDK 1.6 or greater installed and ready to go.
A text editor.
A JDBC Database Driver contained in products such as MySQL or PostgreSQL

Prerequirements to start with JDBC


How to Select Rows from Pandas DataFrame with condition

Question: I have a dataframe (csv file) which consists of about 8000 songs (column name "Song")of e.g. 20 singers(column name "Artist"), so each singer has more than one song. I want to select rows from this dataset that will contain one song of a singer, for example first songs of each singer. So my new pd.dataset will contain 20 songs which singers are different. Please, can anyone help me?
Answer: Well assuming df is your Pandas dataframe you could sort it by Artist and then do something like this:
df = df.drop_duplicates(subset='Artist', keep='first')


Where are all the cats in Arkham City?

Question: You have to use cats to switch between Catwoman and Batman in the main story, but I've seen only seen one group of cats, the ones right next to Catwoman's apartment. It's a hassle to fly back there whenever I want to switch. The game says that there are multiple groups of them, but I can't find more. Where are all of the other cats?
Comment: Aw, now it makes sense out of context without the tag in the title.
Answer: Here are the cat locations in Arkham City:

A close-up:
Comment: Notice how they're on the minimap...
Answer: There's one on the shore near the Joker's side of town.  They should be visible on your minimap with a cat icon
Comment: I'm pretty sure I can't see them on the minimap. A picture would be a great help.
Comment: Sorry, I got distracted at work.  Looks like Mehper got you straightened out though.

Where are all the cats in Arkham City?


Reading multiple FM Radio Channels simultaneously

Question: I'd like to use the Pi to make an FM radio but I also want to be able to read multiple frequencies with the Pi at the same time. Is this possible through using SDR and antenna and software? Or should I look into some sort of physical multiplexor that is compatible with the Pi?
Comment: The SDR reads the whole spectrum (in the range it can cover), but if you can usefully process multiple broadcasts at the same time on the Rpi, I do not know. With just audio it might be possible.
Answer: Devices decoding several transmissions at once are called "skimmers". There are readily available SDR skimmers for continuous wave signals, like telegraphy or Morse code.
Multi-channel FM reception is significantly more complex because of non-trivial modulation. You may take a look at MultiFM project and see if you can get it working on an RPi.


How to format password protected HDD (SATA ?)

Question: What I have tried so far:
- Connect SATA/usb adapter but windows couldn't display the drive.
- Booting with Ubuntu live but couldn't mount the HDD within SATA/usb adapter.
- Direct plug the HDD in another laptop and try to boot with bootable USB but the HDD password prompt always pops up first.
Comment: Is the protection in the disk's BIOS  What is `dmesg` reporting when you connect the disk? Is the MBR readable with `dd` or `hexdump`?
Comment: I'm not sure what you mean "disk's BIOS", but the password is surely on the HDD. When I use "USB Format" I get device write-protected or somthing.
Comment: There are drives that have actual hardware capabilities to set this up and in other cases it might be software that was installed on the drive.
Answer: If the harddisk is protected with the ATA security feature, you need to issue special ATA commands to erase it. Your USB-SATA bridge must pass through these commands, otherwise it won't work.
This article describes how to do a Secure Erase, under the condition you can set the master password (or know the master password).
If you don't know the exact ATA security status of the drive, smartctl -g security /dev/sda etc. will show it.
I don't know how to proceed if you've lost the password and can't set a master password.
Answer: First remove all partitions, then create a partition the OS you're going to use the drive in understands (this 2nd step can be done from the OS itself).
Once you create the partition, it should be possible to format the drive.
If you cannot remove partitions, use a live cd, such as Hiren's Boot CD which has partition managers that should do it.


What is the alternative for magento registry?

Question: Magento registry has been deprecated since Magento V2.3+, what is the new alternative for that?
Answer: No,alternative is available right now.
By using a simple get() and set() function to a class, you can pass to any where at same page. A good example is given by our Dear @vinai at his a module at github. https://github.com/Vinai/module-current-product-example
The class: https://github.com/Vinai/module-current-product-example/blob/master/Registry/CurrentProduct.php#L8
Comment: nice explanation. Thanks for the help
Answer: I don't know your exact use case, so I'll give an example for product only.
What you can do is check if the request has any parameters. If you're dealing with a product page for example, you could get the entity id of the product and then load it via the repository class.
Product page example:
<code><?php declare(strict_types=1);

namespace Your\Namespace;

use Magento\Catalog\Api\Data\ProductInterface;
use Magento\Catalog\Api\ProductRepositoryInterface;
use Magento\Framework\App\RequestInterface;

class ExampleClass
{
    /**
     * @var RequestInterface
     */
    private $request;
    /**
     * @var ProductRepositoryInterface
     */
    private $productRepository;

    public function __construct(RequestInterface $request, ProductRepositoryInterface $productRepository)
    {
        $this->request = $request;
        $this->productRepository = $productRepository;
    }

    public function loadProduct(): ProductInterface
    {
        // Verfify if your're dealing with a product page first
        $entityId = $this->request->getParam('id');
        return $this->productRepository->getById($entityId);
    }
}
</code>
In a lot of cases this can be an alternative to the older registry method to fetch the current product.


Timing error detector used for symbol timing synchronization

Question: The Gardner timing error detector is independent of carrier phase and frequency error, and is also quite immune to self noise (to my understanding, I may wrong about that). Can one assume that it is a recommended  timing error detector for these reasons?
Please if the answer is going to be "it depends on your system" with no further brief input/explanation , then abstain please.
Comment: If you haven't seen this already, please see this post https://dsp.stackexchange.com/questions/31517/location-of-matched-filter/31518#31518 where I detailed my studies on the Gardner Timing Error Detector (TED) vs Mueller & Mueller (M&M) Detector and showed the considerations for each including frequency error.
Answer: It depends on your system :)
Seriously, it depends. Gardner is a pretty solid algorithm with a simple implementation, especially if you're using BPSK or QPSK. It can even be used in some MIMO systems. Its main disadvantage is that it requires two samples per symbol. M&M requires only one, but it has its own disadvantages.
I think that these days the preferred solution is some variation of the polyphase detectors first proposed by fred harris. However, if you're experimenting and building your own system and you want to keep it simple, Gardner is a safe bet.
Comment: The polyphase implementation is not a TED, but an interpolator combined with a matched filter.  What fred harris proposed in his polyphase proposal used a small signal ML approximation TED.  The Gardner TED is an approximation of that TED, FWIW.
Comment: @AndyWalls Gardner TED is not an approximation of an ML TED, that approximation is an early-late TED. Gardner TED is just the non-data-aided version of a zero crossing TED.
Comment: thank you for the brief explanation after the scary comment :"It depends on your system"! :)  ...  is the Polyphase filter bank detector proposed by Fred Harris also independent of phase and frequency error?
Comment: Yes, it also is independent of phase and carrier error.
Comment: For RRC pulse shaped PSK, fred harris recently recommended a band edge filter TED. https://www.researchgate.net/publication/261499267_Band_edge_filters_perform_non_data-aided_carrier_and_timing_synchronization_of_software_defined_radio_QAM_receivers
Answer: Here is a short comparison for your purpose.

The Gardner TED output depends on the excess bandwidth of the pulse shaping filter. Its performance is better if you have moderate to large excess bandwidth.
It is a non-data-aided version of a zero crossing TED. A ZC TED has zero self noise for binary modulation and 100% excess bandwidth, not for all cases.
As you said, the TED output works despite a phase offset or a (small) frequency offset, so it is well suited for timing recovery applications before the carrier recovery (although that can also be divided into stages).
Polyphase clock synchronization is not a TED, it is just a method to do combine matched filtering and interpolation into one operation. Fred used the ML TED for this purpose, you can use zero crossing or Gardner.
M&M is a sort of standard TED when it comes to timing acquisition at 1 sample/symbol. It has zero self noise for any excess bandwidth. However, its performance is very poor for higher excess bandwidths and that makes sense. At 1 sample/symbol and large rolloffs, the pulse sidelobes in time domain are very small and not much useful information can be extracted from them.
Remember that self noise is not everything in a TED. The performance with respect to SNR needs to be taken into account as well.


Being successful in mathematics depends on hard work or intelligence?

Question: I really need to ask this question. Perhaps my question is against the rules of the MSE. I am an IMO participant. I only joined once and I only managed to solve $2$ questions. ($14+1$ points).  I've never had a medal.  My teacher said I should join again. However, after seeing the students who collected $42$ points, I feel very poor. Maybe I will never be like them. I love mathematics. I enjoy solving the question. Teacher said that, if you work harder, you can win a medal. But I know this will upset me more.  That's why I want to stay away from math. I don't want to be a participant again. Really, this is a very sad situation. It feels so bad to know that I'm so inadequate. In the future, I want to choose a field that is not related to mathematics. I don't know what to do.  Maybe I wanted to relax a little bit by writing these. Thank you very much..
Comment: You got 15 points; trust me, others got zilch.  Contest math, and one's performance on one such test is hardly a trustworthy indicator of whether or not to pursue math in future studies, and it is most certainly not a reliable indicator on which to base one's sense of intelligence, competence, creativity, perseverance, grit, dedication, etc.  You're going to make yourself miserable in life if you set your sense of worth and competence on single endeavors like the one you speak of.  If you love math, enjoy it, do well overall, why stay away from math?
Comment: See [Thomas Edison](https://en.wikiquote.org/wiki/Thomas_Edison) : "Genius is one percent inspiration, ninety-nine percent perspiration."
Comment: @MauroALLEGRANZA That's easy to say from someone who already has the genius and who has never experienced being less intelligent :)
Comment: As someone who took part in my country's preselection to the IMO but didn't participate, I'd say that even participating is an achievement (especially if you come from a large country), and getting 15 points is actually not a bad score at all. Congratulations on that!
Comment: I think this [Academia question](https://academia.stackexchange.com/questions/87668/how-do-you-come-to-terms-with-the-fact-that-you-might-never-be-among-the-best-in) could be of interest, as well as the ones linked to it (you don't mention research, but but a lot of the things mentioned there would apply to pretty much any "competitive" situation).
Comment: @Mauro ALLEGRANZA a very impressive saying..
Answer: I think the issue isn't maths, but competition. It isn't unusual to see youngsters in sport who love their sport but hate competing. They don't like the extra pressure, or the possibility of losing so take themselves away from the sport they love. The same is possibly true for you of maths, it's clearly something you enjoy doing, and should carry on doing. But that doesn't mean you should necessarily compete. Try taking some time off competing, still try the questions (if possible), but in your own time, at your own pace, and don't compare yourself to others. See how that goes, and whether or not it reignites your passion.
Edit:
As a side note, don't put down your own achievements. Qualifying in the first place, and collecting $15$ points is no mean feat. You are clearly talented, try and be proud of yourself.
Answer: Solving two questions in an IMO is pretty good! Yes, there will be people who do much better because they've trained extensively, but you shouldn't let it worry you. (There will also be a few people who do much better just by being brilliant, but you shouldn't let that worry you either. Unless you're Terry Tao, there's always going to be a few people like that now matter how far you go in math.)
If you enjoy the problems, that's the most important thing, and I would certainly keep going. The people who are going to be successful in math are those who enjoy doing it. And while it does need you to work hard, it's not the same sort of hard work that people do to train for IMOs, which is very specific to the types of problem that get devised for the IMO and is not really transferable to answering research questions that no-one else knows how to do.
It's also definitely true that comparing how much math people can do in 9 hours is not much like comparing how much they can do in 3 years.


Main Stack Pointer(MSP) vs Process Stack Pointer(PSP)

Question: I was reading the STM32 Programming manual and somewhere on "page 18 " i see these two kind of stack pointers. I always think that there is only ONE stack and therefore only ONE stack pointer to that exists in MCUs and now i'm confused of what these pointers are and what's the difference between theme and each of these is used for what?
Comment: @jonk A friend of mine held a talk on these pointers, and their use in (RT)OSes for Cortex-M microprocessors :https://archive.fosdem.org/2018/schedule/event/multitasking_on_cortexm/
Comment: I can't speak to the STM32 family, as I've only barely used it and then only to prove that a demo board I received (for free) actually worked okay for as few simple things, written in C. However, if I had to guess, they may support two operating modes; one used by a supervisor or operating system and one used by the currently running process. Having two separate stack pointers for those two purposes could offer a few small advantages in some circumstances. Another use might be for a stack pointer and a stack frame pointer. Anyway, I'd need to read up to find out why. Maybe I will.
Comment: @MarcusMüller I'll bookmark it. I just did a quick skim through it and it's got both very general and therefore useful to me information (someday, perhaps) as well as too-specific information that I'll not use because I (almost) ***always*** write my own operating system for embedded work I perform. But looks nice for the general info available and I'll enjoy spending the 3/4 hour, at some point.
Comment: he, nice :) Yeah, the audio was really better there; if you're just into the idea of MSP / PSP, jump to minutes 9 – 12 or so. Always writing your own OS sounds challenging! I do have a very few OSes I like, and for the "most minimal yet deserving the name multi-tasking RTOS", I'd point to ChibiOS. He went to Chromium EC, because he needed something to control power, fan, and stuff in an embedded board with an ARM SoC as main processor. Which was exactly what that OS was designed for (just not for usage in his USRP E-series SDR device, but in a "chromebook" laptop. Details.).
Answer: You are correct in a way, in the cortex m (which your stm32 is, though I can't say which variant unless you specify a part) there is one active stack pointer r13, this can however be either the MSP or PSP.
The reason for two is to enable the user to easily implement a multi tasking 'operating system'.
The idea is that the PSP or process stack pointer is used by the individual tasks, and the kernel uses the MSP.
When an exception happens, a stack frame gets pushed to the currently active stack pointer, and then switches to use the MSP for the exception handler.  In a multi tasking system, if the scheduler caused the exception, it is at this point that you change where the PSP is pointing to be the stack pointer for the next task, and return from the exception. The destacking of the new stack pointer then returns execution to the next task.
If you wish to see an example of code using both, a scheduler I wrote for the Cortex M4f is available on BitBucket, it's not documented, but it is fairly straight forward. A svc instruction is used to start the scheduler, and then pendsv exceptions handle the task switching, the Tick function should be called from a timer to ensure task switching.
Comment: Seemed to me that was the likely explanation, just on principle. Thanks for clarifying the issue.


is there anyway to open sceret network settings in android studio through intent?

Question: I want to develop an android app(using java in android studio) like this https://play.google.com/store/apps/details?id=com.gibatekpro.force4gltemodeonly&hl=en . But the problem I am encountering is that I don't know how to open these settings programmatically. These are mobile settings so there should be an Intent for this. I hope I have explained my problem well. Any help will be appreciated.
Comment: https://stackoverflow.com/a/6789616/5339146 this can help you to start.
Answer: Its an example of opening GPS setting hope you get some help from it
<code>//Declared  as class level constant

public static final int GPS_REQUEST_CODE = 9003;

//Intent wherever you want to set it
  Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                        startActivityForResult(intent, GPS_REQUEST_CODE);

//In On Activity Results

  if (requestCode == GPS_REQUEST_CODE) {

            LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);

            boolean providerEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);

            if (providerEnabled) {
                Toast.makeText(this, "GPS is enabled", Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(this, "GPS not enabled. Unable to show user location", Toast.LENGTH_SHORT).show();
            }
        }
</code>


Need help identifying materials needed to replace rotted and damaged wood

Question: Need the names of materials or any suggestions as to what I should do.
Answer: Underneath the drip-edge is the Fascia board. This is usually 1 x 4 inch stock (looking at your photo).Fascia board can be of any variety of wood or composite although Pine can be painted to protect it from the elements, Redwood and other weather resistant wood species can be used to increase longevity.
Below the Fascia is a Trim molding. This is sometimes used to close large gaps between framing and/or finish pieces or to add more detail to the structure.
Under the Trim is the siding (aluminum or vinyl). The vertical trim piece is missing. It is installed to cover the ends of the horizontal siding and neaten their appearance.
Beside the siding the doors weatherstripping is thrashed and should be repaired or replaced.


What is the difference in OpenVSwitch and openswitch?

Question: Can anybody explain about the main difference in OpenvSwitch(http://www.openvswitch.org/) and Openswitch(http://openswitch.net/). Both of them are open source.
Comment: Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
Answer: Good question.  The 5 second, and facetious answer is that OpenSwitch needs real wires and ports whereas OpenVswitch doesn't.
In more detail: OpenSwitch is switching software that you ultimately deploy onto a physical switch.  Think of it as the equivalent of IOS or CatOS or JunOS.  It's going to be controlling some real hardware ports.  OpenVSwitch, on the other hand, is switching software that you deploy on a virtualized or cloud layer.  There are no hardware ports on this switch: its representation is entirely in software.  For example, when you have two virtual machines running on a compute hosts, talking to one another, their traffic will be crossing a virtual switch.
In even more detail: OpenSwitch expects to use ONIE hardware whereas OpenvSwitch only cares that you have some virtualization plumbing.
There is a lot of work going into SDN and virtualized switching right now.  For example, imagine that you could control the ONIE device by software based on workloads and conditions.  This is your SDN play.  In another domain: how do you get the best possible performance out of a software vswitch when it's running in an environment where the host CPU has to service a bunch of competing tasks?  It's a very interesting area.


Prestashop Geoip module - missing country

Question: No matter how I try I can't find Germany under GeoIP module list in Prestashop 220.127.116.11.
Country is turned on in Localization-> Countries.
I have uploaded newest GeoLiteCity.dat but that hasn't solved the problem.
Any ideas where to look?
Answer: You may have deleted 'Germany' from the countries list on your PrestaShop, you can add it manually under Localization -> Countries in the back office.
Click on 'Add new country' button in the top right corner to open the add new country form and use data in the attached image to fill the form.
Comment: Country was present on that list. I have turned it off and on and now it works!


where to host my react fornt end and express endpoint that interact with smart contract to be fully decentralised?

Question: where to host my react fornt end and express endpoint that interact with smart contract to be fully decentralised. Are there any option to host it decentralised any cloud provider other than traditional centralised options like aws,gcp,azure. IPFS and Storj are file storage i want to run my reactjs fornt end app.
Answer: I'm not sure to correctly understand your question.
If you want to create a fully decentralized application I advise you to read the Ethereum book, chapter 12 : https://github.com/ethereumbook/ethereumbook/blob/develop/12dapps.asciidoc .
Swarm is a good alternative to IPFS to host the frontend in a decentralized way :
https://ethersphere.github.io/swarm-home/ .
According to the Ethereum book :

Due to high gas costs and the currently low block gas limit, smart contracts are not well suited to storing or processing large amounts of data. Hence, most DApps utilize off-chain data storage services, meaning they store the bulky data off the Ethereum chain, on a data storage platform. That data storage platform can be centralized (for example, a typical cloud database), or the data can be decentralized, stored on a P2P platform such as the IPFS, or Ethereum's own Swarm platform.
Decentralized P2P storage is ideal for storing and distributing large static assets such as images, videos, and the resources of the application's frontend web interface (HTML, CSS, JavaScript, etc.).

And :

Swarm is another content-addressable P2P storage system, similar to IPFS. Swarm was created by the Ethereum Foundation, as part of the Go-Ethereum suite of tools. Like IPFS, it allows you to store files that get disseminated and replicated by Swarm nodes. You can access any Swarm file by referring to it by a hash. Swarm allows you to access a website from a decentralized P2P system, instead of a central web server.


What's the difference between 好む and 好き

Question: What's the difference between [好]{この}む and [好]{す}き?
Comment: Difference in grammatical usage? Or difference in meaning?
Answer: First of all, they belong to different word classes. 好き is a na-adjective, and 好む is a transitive verb.

リンゴが好きです。 I like apples.
リンゴを好みます。 I like apples.

Semantically, they both mean "to like [something]", but 好き is much more common in Japanese, and you should be using it most of the time.
In English, there is both a verb version ("I like apples") and an adjective version ("I am fond of apples") to describe this idea, but people usually use the former version. In Japanese, this is different, and we normally use the na-adjective version. In Japanese, 好む is a word that is only sometimes used in stiff sentences.
Answer: 好む/好み = Prefer, or for formal / objective usage
好き = Like, casual and subjective usage
It's safer to use 好む when talking about someone else's tastes. If you need to use like in a business setting, it would be appropriate to use 好み.
Comment: that's useful to me! thank you:)

What's the difference between 好む and 好き


Laying flooring over existing ceramic tile with radiant (hydronic) heat?

Question: We have approximately 4k sq. feet of ceramic terracotta-look tile (late 1980s). We've been wanting, now needing, to update the house but this tile has kept us from doing it. We have a large great room, but can't change the configuration of the kitchen (get rid of old-look counters with bar stool height and put in an island, etc.) because of the tiles. I can't get an answer from contractors as to whether our radiant heat (in slab I think because it's a single-story house) will still provide sufficient heat if we lay something like an interlocking LVP over the tiles. Although tearing up all that tile will be expensive and dirty, we'd do it if need be, but contractors say it may damage the heat.  What can we do? I'm afraid I won't be able to sell the home with this horrible tile (I'd keep it if it were "real," like saltillo/clay/brick, but you can tell it's cheap) and outdated kitchen configuration.  Thank you!
Comment: `interlocking LVP over the tiles` will reduce the heat transfer
Comment: I would try to find a small hidden(maybe under something) section of the floor to see how hard the flooring is to remove.  As @Ruskes said, adding more stuff on top will reduce the heat transfer, but depends on what you need.
Comment: Don't advertise the house as having heated floors, and no one will be surprised if they don't work as advertised.
Answer: If the question is what sells the home, is it how fast it heats up or how ugly the floors are then you know the answer.
Adding low thermal conductive material on top of tiles will slow down the heat transfer, but it will still heat up.
Using interlocking LVP is the winner here. No mess no need to remove the tiles and it will reduce the noise in the room.
Answer: If you've had contractors on site and they've expressed those concerns, I don't think we'll be able to give you a definite answer. Most LVP flooring needs an underlayment anywhere from 1/16" to 1/4" and then the LVP on top of that. The heating will most certainly be reduced. You could get a few samples of the flooring and experiment with the heating and make your own call. You should be able to remove ceramic tile without damaging the heating system if it's in the slab but you'd have to take your time chiseling it up.
Comment: Thank you both. I laid old tiles on top of the current floor and didn't get noticeable heat through. I'm going to get HVAC out to give their thoughts. Given how old the house is, I'm not sure how long the radiant heat will last anyway.
Comment: @Cindy  Very smart thinking.  They keep coming up with better ways to heat the houses.


In Java, why don't we need to mark a class as abstract when we define an interface in it?

Question: If I define a class as
class A {
    interface AL {
        void method ();
    }
}

Then why doesn't the compiler ask me to mark the class as abstract since I have an undefined method in it?
Comment: The method is in the interface not the class.
Comment: It's similar to the concept of a nested class. The syntax is completely legal.
Answer: Since method() is a method of the interface AL, the code works fine. Note that method() is not a method of A, and, therefore, there is no need for the class A to be abstract.
Answer: The method without its implementation is a part of the nested interface declaration. It is not considered a part of the outer class. You might want to take a look at why it is a good idea to have nested interface declarations.
Why should we declare an interface inside a class?
Answer: Consider an example :
Suppose you are creating some application which is concerned with the animal kingdom.
Now you are asked to create a dog, cat, lion etc objects.
So first thing will come to your mind, since these all belong to animal kingdom I can create a base class named ' Animal ', and everything will inherits it. Now yo created something like this
class Animal {
legs;
family;

eat();
roam();
sleep();
makeNoise();
}

So all the animals inheriting the animal class will have these features. You can call this as a "IS-A" relationship. Like Dog IS-A Animal.
Now suppose you are asked to use your animal simulation program for some science-fair. You can use this design in that too.
Now suppose someone asked you to use your simulator in a pet-shop.
Since you don't have any pet behavior. What you did is add the pet features in the base class and thought this will work.
So now you program can create a lion which has the pet behavior. STRANGE!!
Now what you need to put all the pet behavior in one place and make sure that all the pet animals should posses it.
A way to do is create another superclass with all pet features and extend it. This is multiple inheritance, which JAVA don't allow (just Google deadly diamond of death). So comes the interface.
Interface is more like a set of behaviors which your object implements.
And since every object can have its own set of implementations, all these methods should be abstract.
It gives you polymorphic benefits without deadly diamond of death problem. It is a more like a contract which defines that your object must implements following features.
So now what you can do
interface PetBehavior{
  befriend();
  play();
}

and classes from different inheritance tree can implement this interface.
Abstract class gives you a brief idea how a concrete object will may look like but an interface is more like a contract. It tells you what additional features will object will have.