a = np.array([[1,2,3],[4,5,6]])  a[...,::-1] #gives array([[4, 5, 6],[1, 2, 3]])  What is the meaning of ... at here?
This came up in  , but I can't see good documentation or examples that explain how the feature works.
Since the new top bar has been rolled out - a number of different people, established and new users alike, have asked questions on where a specific link has disappeared to with the new top bar design. Where has the link to &lt;X&gt; gone? What are the fundamentals of implementing hook_menu()?  I would like to see the basics covered in a single question, to avoid having to answer the same similar but different questions over and over. Conditional formatting of an entire row based on multiple cells I'm trying to make a conditional formatting rule in Google Spreadsheet that would highlight a row green based on text in multiple cells.   If cells L2, M2, and N2 = APPROVED; and cell O2 = X; then row 2 = highlighted green. Why don't electromagnetic waves require a medium? As I understand it, electromagnetic waves have two components which are the result of each other, i.e., when a moving electric charge creates a changing magnetic field at point X then a changing electric field is created at point Y and this repeating process is what creates EM waves, so therefore, it requires no medium. Is my understanding correct?  One thing that I'm surprised to know is that light is also called an electromagnetic wave.  Does this include light of any kind, for example: light from a bulb, a tube, and also from the Sun? How do they contain electric and magnetic fields? 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. HTTP vs HTTPS performance Rejecting a PhD offer after having accepted it. Advice? I have accepted a PhD offer from a very good university to do a project very close to my interests. I have told the project supervisor I accept it. In the meanwhile I have managed to secure a PhD offer from another 2 universities much better in world rankings and with better research groups and better faculty. Additionally these 2 universities do research exactly on what I want to devote my PhD research.  My only commitment to the first university is a mail confirming I accept. Nothing else. I understand declining the offer after already having accepted it is quite dishonest but it is a huge decision that will affect my future in a very significant level.   I would like your opinion and I would also like to ask for possible consequences of such an action. As far a postdocs concerned, in the first university there is no chance I ever get a postdoc since they do not actually do research on my area (except for the prospective supervisor and even he not as much).  UPDATE I have decided to do as I was afraid to. I have decided to choose a different university than the first one that I have already accepted the offer. My offer acceptance included:    An online "I accept" statement. An e-mail I sent stating "I accept the scholarship and this University is my first option"   I do not have any legal commitments since I have not signed anything. The supervisor of the first university though is really nice to me and continuously was sending me mails. How do I very nicely tell her I will not be joining in the end? Additionally the place I will go in the end will be for research in Mathematics and not Physics. Can I use this as a part of a sensical excuse?  WHAT I HAVE CHOSEN AND WHAT THE CONSEQUENCES WERE  I think that I should let people, especially other beginning grad students know what happened with my case. I have chosen to nicely tell the first university I got accepted that I will not be attending and will not be pursuing a PhD there since I decided I have different research interests (which is true). I had applied there in the first place since I was not sure what I wanted to do and because it was a nice program. Despite that, I got an offer from a World top university to work on 100% my research interests. I explained this to them, the first uni, and they happily let me go and wished me good luck, especially the supervisor who faught a lot secure me funding. I was lucky. Commenting out large sections To &quot;comment out&quot; a line, I need to insert a % at the beginning of the line (so that the line will not be compiled). Is there a way to comment out a large section without having to manually place % in front of each line? How do I get a consistent byte representation of strings in C# without manually specifying an encoding? How do I convert a string to a byte[] in .NET (C#) without manually specifying a specific encoding?  I'm going to encrypt the string. I can encrypt it without converting, but I'd still like to know why encoding comes to play here.  Also, why should encoding even be taken into consideration? Can't I simply get what bytes the string has been stored in? Why is there a dependency on character encodings? How do I definitively show that there are only two propagating degrees of freedom in the Lorenz Gauge $\partial_\mu A^\mu=0$ in classical electrodynamics.  I need an clear argument that   involves the equations of motion for just the potentials $A^0$ and $\mathbf{A}$, and not the electric and magnetic fields.   includes sources $\rho$ and $\mathbf{J}$ in the equations of motion.  This is to justify the assertion that there are degrees of freedom that decouple from the rest of system. does not critically rely on quantum field theoretic arguments (although any supplementary remarks are welcome).     To illustrate the level of clarity I expect, I provide an argument in the Coulomb gauge $\nabla\cdot \mathbf{A} = 0$:  Of the four field degrees of freedom, the gauge condition $\nabla\cdot \mathbf{A} = 0$ removes one degree of freedom (the longitudinally polarized EM waves).  To show that among the remaining three degrees of freedom only two are propagating, consider the field equations of motion in the Coulomb gauge:  \begin{align} \nabla^2 A^0 &amp;= -\rho/\epsilon_0,\\ \big[\frac{1}{c^2}\frac{\partial^2}{\partial t^2}-\nabla^2\big]\mathbf{A}&amp;= \mu_0 \mathbf{J}-\nabla \frac{1}{c^2}\frac{\partial}{\partial t}A^0. \end{align}  The first equation is NOT a wave equation for $A^0$, and thus does not propagate.  The final equation IS a wave equation, and describes the propagation of two degrees of freedom (Gauss' law in first eq. can be solved, and then inserted into the second equation to show that $\mathbf{A}$ only couples to the Solenoidal part of the current). I am looking for a book about "advanced" classical mechanics. By advanced I mean a book considering directly Lagrangian and Hamiltonian formulation, and also providing a firm basis in the geometrical consideration related to these to formalism (like tangent bundle, cotangent bundle, 1-form, 2-form, etc.).  I have , but I would like to go into more details about the [symplectic] geometrical and mathematical foundations of classical mechanics.  Additional note: A chapter about relativistic Hamiltonian dynamics would be a good thing. I need some help in relation to this exercise    "Prove that if a normal subgroup $H$ of $ G$ has index $n$, then $g^n \in H$ for all $g \in G$."  I'm not allowed to use quotient groups in the proof, because the exercise is in the chapter before.   I tried by induction on $n$. The case $n=1,n=2$ are obvious, but even  the case $n=3$ is giving me trouble so I give up studying the general case of the inductive step.  My other approach was studying left or right coset of $G$. But I only proved that if $g \in aH$ then $g^2 \notin aH$ if $a \notin H$, and I can't find a way to demonstrate that $g^n \in H$. (my starting idea was to prove that every power of $g$ is in a different coset but then I realize that in this way I don't handle several case, for example $g$ has period strictly lesser than $n$ and in conclusion it doesn't prove the exercise)  Maybe I'm missing something about indexes, and this is why I asked here for some help,  (I can't use quotient groups because they are introduced later than this exercise, forgot to add this info in the beginning) Thanks in advance :) How do I unlock the Dream Suite in Animal Crossing New Leaf? Is there a difference between taking a far shot on a 50mm lens and a close shot on a 35mm lens? Keyboard shortcut to autocomplete the user in comments As I was trying to validate our pcb design, I measured the impedance matching on the digital transmission lines, and got stuck with the oscilloscope not showing what I expected. We are using the PicoScope 4227, but I suspect that the strange measurement is not directly related to the specific oscilloscope but more to general on how to measure digital signals.  My setup is as follow: I measure the output-pin of an FPGA with both oscilloscope input A and B.  Input A (blue) is measured using the oscilloscope probe set to x10.  Input B (red) is measured using a 50-ohm coxial cable terminated at the scope input with 50-ohm.  As you can see, Input B seems correct, no reflection ect.  But Input A (the probe) has some overshoot, and ringing.  The probe should be calibrated and valid to 250MHz, so I don't get was is wrong. ?  I suspect that the small probe-clip adds some inductance, and therefore we see the ringing. But I really don't know.    EDIT After reading your answers, I walked got into our lab storage and started looking, and found a probe GND clip like the one showed in the answer below.   When I use that clip, I get the output below. Which is really a huge improvement. I have a requirement to implement an "Unsaved Changes" prompt in an ASP .Net application.  If a user modifies controls on a web form, and attempts to navigate away before saving, a prompt should appear warning them that they have unsaved changes, and give them the option to cancel and stay on the current page.  The prompt should not display if the user hasn't touched any of the controls.  Ideally I'd like to implement this in JavaScript, but before I go down the path of rolling my own code, are there any existing frameworks or recommended design patterns for achieving this?  Ideally I'd like something that can easily be reused across multiple pages with minimal changes. Keeping track of programs When I install a simple program it often uses make &amp;&amp; make install and doesn't often even have an uninstall target.  If I wish to upgrade a program, is it standard protocol to assume it just rewrites seamlessly over the old program?  How do I keep track of these programs; do most people just 'fire and forget' and if no uninstall target is given do I have to manually delete everything? Difficulty in creating macro '\newcommand' for the beginning and end of frames in Beamer Schedule to open website I'd like to open a website at regular intervals per day, i.e., the browser should open and automatically navigate towards a pre-set URL.  I looked at options like scheduling to open browser, but I can't figure out how to open it with a default URL. (No I do not want to make this my start page)  Any help is appreciated