Ajax response to be a return value of a function
How do I return the response from an asynchronous call?
What is the exact use of the symbols $\partial$, $\delta$ and $\mathrm{d}$ in derivatives in physics? How are they different and when are they used? It would be nice to get that settled once and for all.  $$\frac{\partial y}{\partial x}, \frac{\delta y}{\delta x}, \frac{\mathrm{d} y}{\mathrm{d} x}$$   For what I know, $\mathrm{d}$ is used as a small infinitisemal change (and I guess the straight-up letter $\mathrm{d}$ is usual notation instead of italic $d$, simply to tell the difference from a variable). Of course we also have the big delta $\Delta$ to describe a finite (non-negligible) difference. And I have some vague idea that $\partial$ is used for partial derivatives in case of e.g. three-dimensional variables. Same goes for $\delta$, which I would have sworn was the same as $\partial$ until reading this answer on Math.SE:    Then to make the confusion total I noticed an equation like $\delta Q=\mathrm{d}U+\delta W$ and read in a physics text book that:     The fact that the amount of heat [added between two states] is dependent on the path is indicated by the symbol $\delta$...   So it seems $\delta$ means something more? The text book continues and says that:     a function [like the change in internal energy] is called a state function and its change is indicated by the symbol $\mathrm{d}$...   Here I am unsure of exactly why a $\mathrm d$ refers to a state function.   So to sum it up: down to the bone of it, what is $\delta$, $\partial$ and $\mathrm{d}$ exactly, when we are talking derivatives in physics.  Addition  Especially when reading a mathematical process on a physical equation like this procedure:  $$\delta Q=\mathrm{d}U+p\mathrm{d}V \Rightarrow\\ Q=\Delta U+\int_1^2 p \mathrm{d}V$$  It appears that $\delta$ and $\mathrm{d}$ are the same thing. An integral operation handles it the same way apparently? We know (from the accidents that happened between 1999-2005) that      The Sith rely on their passion for their strength. They think inward, only about themselves.   and we also know that     Always two there are, no more, no less. A master and an apprentice.   And from the EU, we know that each Sith apprentice will (try to) kill and replace their master at some point, in order to become the one who bundles the entirety of the Sith power (so to say).    Q1: Given these points, why do Sith bother to take up apprentices at all? It doesn't make sense to pass on their knowledge of the dark side, because they only care about themselves, and it would also contradict this philosophy to teach competition that will endanger their power and ultimately their life.    Q2: As a special case of this question in The Empire Strikes Back, Vader tries to turn Luke by saying     Luke, you can destroy the Emperor. He has foreseen this. It is your destiny. Join me, and together we can rule the galaxy as father and son.   (emphasis by me)  Now, the same question rises: If the Emperor has foreseen that Luke can destroy him, why would he want Luke to become a Sith? Does installing many programs really slow down Windows? Omission of "the" in "elected him president" and "made captain" Why is there no the before president and captain?     They elected him president.       She was made captain of the team. My understanding is that a random variable is actually a function $X: \Omega \to T$, where $\Omega$ is the sample space of some random experiment and $T$ is the set from which the possible values of the random variable are taken.  Regarding the set of values that the random variable can actually take, it is the image of the function $X$. If the image is finite, then $X$ must be a discrete random variable. However, if it is an infinite set, then $X$ may or may not be a continuous random variable. Whether it is depends on whether the image is countable or not. If it is countable, then $X$ is a discrete random variable; whereas if it is not, then $X$ is  continuous.  Assuming that my understanding is correct, why does the fact that the image is uncountable imply that $Pr(X = x) = 0$.  I would have thought that the fact that the image is infinite, regardless of whether it is countable or not, would already imply that $Pr(X = x) = 0$ since if it is infinite, then the domain $\Omega$ must also be infinite, and therefore  $$Pr(X = x) = \frac{\text{# favorable outcomes}}{\text{# possible outcomes}} = \frac{\text{# outcomes of the experiment where X = x}}{|\Omega|} = \frac{\text{# outcomes of the experiment where X = x}}{\infty} = 0$$  What is wrong with my argument?  Why does the probability that a continuous random variable takes on a specific value actually equal zero? How long can eggs be unrefrigerated before becoming unsafe to eat? Total time derivatives and partial coordinate derivatives in classical mechanics How to check if an object is nullable? How do I check if a given object is nullable in other words how to implement the following method... bool IsNullableValueType(object o) {     ... }  I am looking for nullable value types. I didn't have reference types in mind. //Note: This is just a sample. The code has been simplified  //to fit in a post.  public class BoolContainer {     bool? myBool = true; }  var bc = new BoolContainer();  const BindingFlags bindingFlags = BindingFlags.Public                         | BindingFlags.NonPublic                         | BindingFlags.Instance                         ;   object obj; object o = (object)bc;  foreach (var fieldInfo in o.GetType().GetFields(bindingFlags)) {     obj = (object)fieldInfo.GetValue(o); }  obj now refers to an object of type bool (System.Boolean) with value equal to true. What I really wanted was an object of type Nullable&lt;bool&gt; So now as a work around I decided to check if o is nullable and create a nullable wrapper around obj. Recently I began studying machine learning, however I failed to grasp the intuition behind .   The following are the facts about logistic regression that I understand.   As the basis for hypothesis we use . I do understand why it's a correct choice, however why it's the only choice I don't understand. Hypothesis represents the probability that the appropriate output is $1$, therefore the domain of our function should be $[0,1]$, this is the only property of sigmoid function I found useful and appropriate here, however many functions satisfy this property. In addition, sigmoid function has a derivative in this form $f(x)(1-f(x))$, but I don't see the utility of this special form in logistic regression.   Question: what so special about sigmoid function, and why we cannot use any other function with domain $[0,1]$? The cost function consists of two parameters ${\rm Cost}(h_{\theta}(x),y)=-\log(h_{\theta}(x))$ if $y=1, {\rm Cost}(h_{\theta}(x),y)=-\log(1-h_{\theta}(x))$ if $y=0$. In the same was as above, I do understand why it's correct, however why is it the only form? For example, why couldn't $|h_{\theta(x)}-y|$ be a good choice for the cost function?  Question: what is so special about the above form of cost function; why cannot we use another form?   I would appreciate if you could share your understanding of logistic regression. Product of path connected spaces is path connected 'bridges' on a PCB copper layer I've come across a design where each pad was connected using 4 'bridges' to the GND copper layar. What stands behind these 'bridges'? Why not make a full copper layer with only solder-mask defining the pads? I have a dataset with a large number of Yes/No responses. Can I use principal components (PCA) or any other data reduction analyses (such as factor analysis) for this type of data? Please advise how I go about doing this using SPSS. Am I required to pay UK/ USA Visa fees if I have a German residence permit? Here is the situation. I am non-european but staying in Germany with a Residence permit. I can visit all Schengen listed countries with no issue. Assuming that I would want to travel to a non-Schengen country e.g. UK or USA, can I use my residence permit to travel there or am I required to apply as a citizen of my country? Assuming Germans are not required to pay Visa fees to that country, will I have to pay since I only have a residence permit? Third case, Europeans can fly directly to the airport of some countries and apply for a visa from there. In some other countries, you are required to book a Visa appointment at the embassy, which may be granted or not. Does that apply for one with a residence permit? How can I make a peer-to-peer multiplayer game? How can I make a p2p multiplayer game? I would like to have a server-less multiplayer game. But then, how all the clients know each other?  Why the p2p-protocol is so famous in file transfer but not in multiplayer games? Auto confirm when running bash scripts? Origins of Tension First of all, I have a confusion about the definition and idea of Tension. For example, in my Physics Textbook, the idea of tension is written like this: &quot;Let's say there is a wire with a cross-section area of A and its length is $L_o$. If I hang the wire from a point and hang a weight of W on the other end of the wire, it will generate a repulsive force of T. This T is called the Tension Force.&quot; For me, this only explains to me what force will we call tension force, but it doesn't quite explain to me what is exactly this Tension force or where it originates from. Also, I have been doing pulley problems (Figuring out the acceleration of weights hanging from pulleys)  by first labeling all of the tension forces by $T_1$, $T_2$, and then doing some math with them to get my answer. But It bugs me that I am using these tension force values without even knowing where they came from or what they are. My idea was, maybe Tension force comes from the intermolecular bonds between the molecules of the rope, rubber or wire, etc. But even then, I have some different situational questions. For example:  Why you can't push a rope, copper wire against a wall?  What happens when I pull on two ends of a wire with 2 different forces?  Does the force increase proportionally to the applied force? Why does the wire break after a certain amount of force is exceeded.?  Does the idea of tension apply to everyday objects,(for example, a coffee mug, glass pane, etc). If it does, can I use something like a heat map or 3D equation to describe the tension in every point of the object? [Edit: more concisely, is there a mathematical way to show the various amounts of tension forces on a 2D (like a metal sheet) and 3D objects (like a football ) instead of a 1D object(like a string)].  If I take a metallic object like a paperclip or a thin wire. I can bend It multiple times and it eventually breaks into two pieces. I used to do this to pull of capacitors from old circuit boards. But does it happen with things like ropes or paper? If not, why it doesn't happen? ( Maybe it has something to do with intermolecular forces and the various internal stresses?)  Let's say I have an iron bar and I have thrown it out into space. Does that iron bar have equal stress distribution or still uneven or will the stress on all points become zero? (Is there even such thing as zero stress?) In The Last Jedi:     The Resistance fleet is tracked through hyperspace by the First Order after they make their jump away from their old base.   As soon as the FO ships appear, the Resistance immediately come to the (correct) conclusion as to the tech that was used.  Why would they assume the use of this tech, that they have never encountered before, as opposed to the more common technique of     tracking a ship through the use of a homing beacon. After the latest Ubuntu updates, I have not been able to open virtualbox, on starting it gives me an error saying the kernel driver is either not loaded or set up properly and that I should reinstall virtualbox-dkms package. After removing virtualbox, and trying to reinstall I get the error below: ERROR: Cannot create report: [Errno 17] File exists: '/var/crash/virtualbox-dkms.0.crash' Error! Bad return status for module build on kernel: 5.8.0-34-generic (x86_64) Consult /var/lib/dkms/virtualbox/6.1.10/build/make.log for more information. dpkg: error processing package virtualbox-dkms (--configure):  installed virtualbox-dkms package post-installation script subprocess returned error exit status 10 dpkg: dependency problems prevent configuration of virtualbox:  virtualbox depends on virtualbox-dkms (&gt;= 6.1.10-dfsg-1~ubuntu1.20.04.1) | virtualbox-source (&gt;= 6.1.10-dfsg-1~ubuntu1.20.04.1) | virtualbox-modules; however:   Package virtualbox-dkms is not configured yet.   Package virtualbox-source is not installed.   Package virtualbox-modules is not installed.   Package virtualbox-dkms which provides virtualbox-modules is not configured yet.  dpkg: error processing package virtualbox (--configure):  dependency problems - leaving unconfigured dpkg: dependency problems prevent configuration of virtualbox-qt:  virtualbox-qt depends on virtualbox (= 6.1.10-dfsg-1~ubuntu1.20.04.1); however:   Package virtualbox is not configured yet.  dpkg: error processing package virtualbox-qt (--configure):  dependency problems - leaving unconfigured No apport report written because the error message indicates it's a follow-up error from a previous failure.                             No apport report written because the error message indicates it's a follow-up error from a previous failure.                                                         Processing triggers for menu (2.1.47ubuntu4) ... Processing triggers for bamfdaemon (0.5.3+18.04.20180207.2-0ubuntu2) ... Rebuilding /usr/share/applications/bamf-2.index... Processing triggers for desktop-file-utils (0.24-1ubuntu3) ... Processing triggers for mime-support (3.64ubuntu1) ... Processing triggers for hicolor-icon-theme (0.17-2) ... Processing triggers for gnome-menus (3.36.0-1ubuntu1) ... Processing triggers for systemd (245.4-4ubuntu3.3) ... Processing triggers for man-db (2.9.1-1) ... Processing triggers for shared-mime-info (1.15-1) ... Errors were encountered while processing:  virtualbox-dkms  virtualbox  virtualbox-qt E: Sub-process /usr/bin/dpkg returned an error code (1)  This happens even when I boot from the previous kernel using the grub menu, any help would be very appreciated. I have also tried to use aptitude to remove any conflicting versions of virtualbox from other repositories but still the same issue. What's the difference between an id and a class? JavaScript window resize event