Given a problem, how does one know whether to use quantum mechanics or classical mechanics?   Take for example electron scattering from a nucleus. The electrons are given a wavefunction in this case. Why not use the classical approach?
Is there any parameter (in terms of physical quantities such as mass, length, charge...) which can be used to decide when to treat a system quantum mechanically and not classically?
I'm training a neural network but the training loss doesn't decrease. How can I fix this?  I'm not asking about overfitting or regularization. I'm asking about how to solve the problem where my network's performance doesn't improve on the training set.    This question is intentionally general so that other questions about how to train a neural network can be closed as a duplicate of this one, with the attitude that "if you give a man a fish you feed him for a day, but if you teach a man to fish, you can feed him for the rest of his life." See this Meta thread for a discussion:   If your neural network does not generalize well, see: New database server hardware and software inserts slower than old setup How does Windows know whether it has internet access or if a Wi-Fi connection requires in-browser authentication? In Windows 7, the notification area networking icon will show an error indicator if there is no internet access , and the error icon goes away once there is a successful connection to the internet . Sometimes, if the WiFi connection requires an in-browser authentication step, like on many guest networks in hotels or universities, then the following pop-up bubble appears, saying as much:    How does Windows know whether or not it has a successful internet connection? Presumably it is checking some online Microsoft service to see whether it has a successful connection, gets redirected to some other page, or doesn't get any response at all, but I haven't seen anywhere that this process or the services used are documented. Can anybody explain how this works? I would prefer answers that refer to facts, rather than just guessing, but if you have a really good guess, then go for it.     This question was a .   Read the May 16th, 2011  for more details or  Question of the Week. Is it possible to make LaTeX mark overfull boxes in the output, for example by drawing red rectangles in the PDF where the boxes overflow? The purpose -- to more easily "see" where the problems are in the output. I was just wondering whether the following statement is correct.  Let R be a ring and M a noetherian R module. Then M is finitely generated. I use Thunderbird to backup my web-based email account: I open Thunderbird and copy the mail messages from the Inbox to a local folder.   Is there a way to do this automatically every day, so that I don't have to open Thunderbird all the time?  EDIT:  is very useful for GMail accounts. For non-GMail account, the getmail method should probably be used. Move iTunes folder outside Music folder iTunes by default stores its settings, the iTunes Library.itl file, and the music library audio tracks, inside the \Users\username\Music\iTunes folder.  I don't want my Music folder polluted with program settings, especially because I'm synchronizing that folder on the cloud. Via the settings panel I can only change the path of the audio tracks, but the settings remain in the default position.  Is there a way to completely move the iTunes folder to another path?  PS: I've looked at the answers to , but the focus there is on moving the media library only, not the whole iTunes directory. Why is 3D stress tensor acting only on three surfaces? I'm trying to learn about the stress tensor (in 3D)    The tensors are said to have directions (the first subindex $i$ in $\sigma_{ij}$) and specify the surface upon which they act (the second subindex $j$ in $\sigma_{ij}$).  What confuses me is why is it defined only to act on three surfaces, even when the cube has six surfaces? Lightning: why can you not have an expression combined with text in an HTML attribute? So, I've been struggling with this for a while, trying to figure out how to get it to work. Here is what I originally did:  &lt;button class="btn btn-primary {!v.isLink1 ? 'active' : ''}"&gt;   And so on. Here's the documentation on it.   However, when you actually try to save this in the developer console, you get the error:  Field Integrity Exception: Failed to save undefined: Cannot mix expression and literal string in attribute value, try rewriting like {!'foo' + v.bar}: Source   I finally figured out that you have to put all of the classes inside of the expression, like so:  &lt;button class="{!v.isLink1 ? 'btn btn-primary active' : 'btn btn-primary'}"&gt;   This doesn't seem very intuitive. It's also not documented anywhere I could find. Could someone explain to me why it is this way and if it will ever change?   (and hopefully this question saves someone some headaches in the future) I have a program in which I've lost the C++ source code.  Are there any good C++ decompilers out there?  I've already ran across . Images as Planes in Eevee having weird transparency One Object won't Show up in Final Render even though it shows up in the Preview Render I have a model of a building with a sidewalk around it.  Both show up when I switch to rendering mode in both Blender Render and Cycles Render mode.  But:  when I hit F12 for a final proper render, the building shows up -- but the sidewalk doesn't.    I've checked the normals and I thought the normals seemed pointed in the right direction.  I've set the Clipping on the Camera to a high number.  I removed all the materials from the sidewalk and added a new material-- the problem persists.  I've exported the blend as an FBX file and the Sidewalk shows up fine in Unity.  Just in final renders, it doesn't show up.    Here is a blend file: .  I tried to destroy everything unrelated to the issue and label things in a clear way.    Thanks. How do I implement a draggable tab using Java Swing? Instead of the static JTabbedPane I would like to drag-and-drop a tab to different position to rearrange the tabs.  EDIT: . I have installed nodeJS on Ubuntu with following code   sudo apt-get install nodejs   Since I am a new user for ubuntu I also ran this code too  sudo apt-get install npm   Now when I type    nodejs --version   It shows   v0.6.19   I checked and saw latest nodeJS version is 0.10.26   How can I update my version of nodeJS to 0.10.26?  I tried with    sudo apt-get install &lt;packagename&gt;  sudo apt-get install --only-upgrade &lt;packagename&gt;   but no luck. In Windows, 'removable' drives cannot be partitioned, without the partitions not appearing and receiving drive letters, apart from the first partition.  Partitioned flash drives work fine in Linux.  What I want to do is partition a 8GB flash drive into two, with the first partition containing various boot disc images, which can be selected to boot from, and have various portable apps, documentation, utilities, scripts, etc, on the other partition.  I currently do this using two separate flash drives, but I want to be able to use a single flash drive for everything, which I keep on my keyring.  It is not possible to do this without having at least two partitions, as the ISO boot selector for the boot disc images will not work otherwise.  I know there is a method where you can flip a bit, using Lexar's USB Format Tool, which fools Windows into thinking that the partitions are on a fixed hard drive.  However, this apparently makes it difficult to eject the flash drive.  Flash drives with  from SanDisk had two partitions, presenting itself to the host system as a USB hub with a CD drive and standard USB mass storage device attached.  This is what I would like to emulate, if possible. Optimal bcrypt work factor SMTP 25 closed even though I allow everything in firewall (Debian server running sendmail) I am running sendmail + dovecot in my Debian server. I have enabled the firewall rules to allow everything:   iptables -P INPUT ACCEPT   iptables -P OUTPUT ACCEPT   iptables -P FORWARD ACCEPT   iptables -F   iptables -X  However after a quick check at yougetsignal.com, my port 25 is still being blocked. But 143, 80 are okay. What do the fields in ls -al output mean? The ls -al command shows the following output;  -rwxrw-r--    10    root   root 2048    Jan 13 07:11 afile.exe   What are all the fields in the preceding display? Does excessive markup affect SEO? reversing plot axis for Plot, LogPlot, LogLogPlot