How to check that a parameter was supplied to a bash script
Check existence of input argument in a Bash shell script
Intuitive understanding of the derivatives of $\sin x$ and $\cos x$ One of the first things ever taught in a differential calculus class:   The derivative of $\sin x$ is $\cos x$. The derivative of $\cos x$ is $-\sin x$.   This leads to a rather neat (and convenient?) chain of derivatives:   sin(x) cos(x) -sin(x) -cos(x) sin(x) ...   An analysis of the shape of their graphs confirms some points; for example, when $\sin x$ is at a maximum, $\cos x$ is zero and moving downwards; when $\cos x$  is at a maximum, $\sin x$ is zero and moving upwards.  But these "matching points" only work for multiples of $\pi/4$.  Let us move back towards the original definition(s) of sine and cosine:  At the most basic level, $\sin x$ is defined as -- for a right triangle with internal angle $x$ -- the length of the side opposite of the angle divided by the hypotenuse of the triangle.  To generalize this to the domain of all real numbers, $\sin x$ was then defined as the Y-coordinate of a point on the unit circle that is an angle $x$ from the positive X-axis.  The definition of $\cos x$ was then made the same way, but with adj/hyp and the X-coordinate, as we all know.  Is there anything about this basic definition that allows someone to look at these definitions, alone, and think, "Hey, the derivative of the sine function with respect to angle is the cosine function!"  That is, from the unit circle definition alone.  Or, even more amazingly, the right triangle definition alone.  Ignoring graphical analysis of their plot.  In essence, I am asking, essentially, "Intuitively why is the derivative of the sine the cosine?" Why is the amount of photos that fit on one card dependent on ISO? In , I used quotes to demark specific terms, but after I posted the question, I wondered if I'm doing it right.  Usually, when quoting something a person says, the quotation mark goes after the comma or period, like so:     "This is my opinion," she said.   However, I sometimes use quotes not to represent something said by anyone, but instead for delineating a set term or phrase to make it clear that those words go together and none of them should be mistaken for a part of the rest of the sentence. Like this:     Should I say "stand up", "standup", or "stand-up"?   This looks weird to me:     Should I say "stand up," "standup," or "stand-up"?   ... but maybe I'm wrong about the rules.  Is it correct to use quotes in this way? And if so, are the quotes positioned correctly relative to the other punctuation marks?  Are there other alternatives for delineating terms without the use of quotes? A question about causality and Quantum Field Theory from improper Lorentz transformation If $x^{2}-x\in Z(R)$ for all $x\in R$, then $R$ is commutative. Why is free will a widely discussed, established concept? Does this concept emerge from religious / spiritual doctrine? Why is there so much interest in this topic?  If a neural-network based AI machine with a certain high degree of complexity scores a perfect 100 every run in a turing test, have we not already refuted the idea of free will? In fact, let me extend this reasoning, if ANY machine scores a single point in a turing test (and not 100), have we not already disproved (or alternatively put in great doubt the existence of) free will? If we already created a machine that can master a certain degree of human interaction, have we not then demonstrated that human interaction is programmable? (given enough time for the creation of a complex or more appropriately elaborative neural system).   From the perspective of an external observer, such a machine would be qualitatively human although intrinsically quantitative behind a stream of 1's and 0's. It would exhibit a type of decision making indistinguishable from that of a human. Does this not reduce the type of decision making we understand to be "free will" to something quantitative, deterministic, materialist? How many ways can $r$ nonconsecutive integers be chosen from the first $n$ integers? I try to add an item to my sharepoint list from a custom web part. Is there any mistake in my code?  [WebMethod]         public static string AjouterDemande()         {             SPList ListeDemandeConge = SPContext.Current.Site.RootWeb.Lists["DEMANDE CONGÉ"];             SPListItem ListItem = ListeDemandeConge.Items.Add();             ListItem["CODE"] = code;             ListItem["DEMANDEUR"] = Utilisateur.LoginName;             ListItem["DATE DEMANDE"] = DateTime.Today.Date;             ListItem["DATE FIN"] = EndDateD;             ListItem["DATE DEPART"] = StartDateD;             ListItem["DUREE"] = int.Parse(DayCount);             ListItem["PREMIER RESPONSABLE"] = Employe.FirstSuperior.LoginName;             ListItem["DEUXIEME RESPONSABLE"] = Employe.SecondSuperior.LoginName;             ListItem["PRESENCE PRES"] = Boolean.Parse(FirstRespPresent);             ListItem["SOLDE CONGE"] = Conge.SoldeAnneeConge;             ListItem["MOIS"] = int.Parse(StartDateTab[1]);             ListItem["ANNEE"] = int.Parse(StartDateTab[0]);             ListItem["JOURS APPROUVEES"] = 0;             ListItem.Update();             ListeDemandeConge.Update();             return "true";          }   When I use F10 to process debugging step by step and get to my listitem.update(), it went out without giving any error. Finding value of $S-T$ in $2$ binomial sum. If $\displaystyle S=\sum^{n}_{k=0}(-1)^k\frac{1}{k+m+1}\binom{n}{k}$ and f $\displaystyle T=\sum^{m}_{k=0}(-1)^k\frac{1}{k+n+1}\binom{m}{k}$.Then $S-T$ is   Try:$$S=\sum^{n}_{k=0}(-1)^k\int^{1}_{0}x^{k+n}\binom{n}{k}dx=\int^{1}_{0}x^n\sum^{n}_{k=0}(-x)^k\binom{n}{k}dx$$  Could some help me, thanks Boot problem after hanging and manual power off ( Stopping User Manager for UID 121... ) My Ubuntu stalled while running Android's VirtualBox version, so I powered off the system. But after reset it stopped during this line:     Stopping User Manager for UID 121... _ So i googled it and have read  question and tried these steps:  Boot into Recovery Mode, drop to a root shell, and follow the steps below:   Run mount -o rw,remount / to mount the drive in Read-Write mode.Run sudo apt-get purge nvidia-* to purge the NVIDIA driver.You may also need to purge xserver-xorg and reinstall it, which will  require you to enable networking in Recovery.Reboot. You may have to add the nouveau.modeset=0 flag in GRUB to boot properly (Check my Q&amp;A for specifics).   You should be past the screen flicker and be at your desktop.  But in doing this step:  Now reinstall the NVIDIA drivers the proper way:sudo apt-get install  nvidia-367 (or 340, 352, 364, 370, whichever works).Reboot again.  I found i have not internet, and my WiFi is not in ifconfig list!!! By running :     Iw wlp2s0 scan   I get :  N180211 not found I also search for it and not understand why WiFi gone off. Now i thinking to use live USB of ubuntu to download NVIDIA and xserver-xorg and the install the by dpkg command during tty2. Update : in Ubuntu live i have this settings :  ubuntu@ubuntu:~$ sudo lshw -c video   *-display                         description: VGA compatible controller        product: HD Graphics 620        vendor: Intel Corporation        physical id: 2        bus info: pci@0000:00:02.0        version: 02        width: 64 bits        clock: 33MHz        capabilities: pciexpress msi pm vga_controller bus_master cap_list rom        configuration: driver=i915 latency=0        resources: irq:129 memory:a2000000-a2ffffff memory:b0000000-bfffffff ioport:6000(size=64) memory:c0000-dffff   *-display        description: 3D controller        product: GM108M [GeForce 920MX]        vendor: NVIDIA Corporation        physical id: 0        bus info: pci@0000:03:00.0        version: a2        width: 64 bits        clock: 33MHz        capabilities: pm msi pciexpress bus_master cap_list        configuration: driver=nouveau latency=0        resources: irq:128 memory:a3000000-a3ffffff memory:90000000-9fffffff memory:a0000000-a1ffffff ioport:3000(size=128)  and ubuntu@ubuntu:~$ sudo lshw -c display   *-display                         description: VGA compatible controller        product: HD Graphics 620        vendor: Intel Corporation        physical id: 2        bus info: pci@0000:00:02.0        version: 02        width: 64 bits        clock: 33MHz        capabilities: pciexpress msi pm vga_controller bus_master cap_list rom        configuration: driver=i915 latency=0        resources: irq:129 memory:a2000000-a2ffffff memory:b0000000-bfffffff ioport:6000(size=64) memory:c0000-dffff   *-display        description: 3D controller        product: GM108M [GeForce 920MX]        vendor: NVIDIA Corporation        physical id: 0        bus info: pci@0000:03:00.0        version: a2        width: 64 bits        clock: 33MHz        capabilities: pm msi pciexpress bus_master cap_list        configuration: driver=nouveau latency=0        resources: irq:128 memory:a3000000-a3ffffff memory:90000000-9fffffff memory:a0000000-a1ffffff ioport:3000(size=128)  and : ubuntu@ubuntu:~$  cat /etc/os-release NAME=&quot;Ubuntu&quot; VERSION=&quot;18.04.3 LTS (Bionic Beaver)&quot; ID=ubuntu ID_LIKE=debian PRETTY_NAME=&quot;Ubuntu 18.04.3 LTS&quot; VERSION_ID=&quot;18.04&quot; HOME_URL=&quot;https://www.ubuntu.com/&quot; SUPPORT_URL=&quot;https://help.ubuntu.com/&quot; BUG_REPORT_URL=&quot;https://bugs.launchpad.net/ubuntu/&quot; PRIVACY_POLICY_URL=&quot;https://www.ubuntu.com/legal/terms-and-policies/privacy-policy&quot; VERSION_CODENAME=bionic UBUNTU_CODENAME=bionic  please consider the above three output has token form Ubuntu live flash system. What do you suggest and what do you think about reason of this failure? Also do you think it must be reported by me in ubuntu site, or it will be done automatically? Thanks. facl ignoring the "x" permission but only on files Why is Harry Potter a half-blood? Being born to James and Lily, how can Harry be called a half-blood?  It is said that admission in Hogwarts is given to children of Muggles when they show magical talents as a child, and Lily was no exception to this. This makes Lily a witch, so why is Harry half-blooded? How can I install the Google Apps Package (Play Store, ...) on my Android device? There has been a significant drop (90%) in traffic from Google to one of my well-established sites (6+ years) in the last week. Searches show that the top 3 wide keywords all dropped 4 spots. Searches for other keywords do not show ANY results in the first 10 to 25 pages of results, while previously one 1st or 2nd page at most.  Since there are , the question really is:  What steps are necessary to figure out what caused such a drop?  There have been no major changes during this period or the last month on the site and certainly not in the homepage which has dropped in rank. Over all the years of running this site and plenty of others, I have never experienced this. There are is duplicate content on my site and I have rigorously used canonical links for the last few years to ensure it is not misinterpreted as such. Difference between "right of=" and "right=of" in PGF/TikZ In the PGF/TikZ manual, sometimes I see the option right of=somenode instead of right=of somenode. They look very similar, but the effects are different.  The distance between nodes positioned with the latter option is boundary-to-boundary, as stated in the manual. However, with the first option, it seems that the distance is shorter. I couldn't find any explanation of the first option in the manual.  My question is: what is the difference between the two options? Is there any explanation in the manual that I missed? Function overloading in C If I live in the US, for example, where current interest rates are practically nil, how can I take advantage of the fact that ? Powers of infinite cardinals in the generic extension existence of sequence of polynomial Is there a sequence of polynomials $P_n$ such that   $\displaystyle\lim_{n \to \infty} P_n(z) = \begin{cases} 1, &amp; \text{Im } z &gt; 0\\ 0, &amp; z \text{ is real,} \\ -1, &amp; \text{Im } z &lt; 0 \end{cases}$  I have no clue where to start from. Please provide some hints. Thanks in advance. How do you find out the caller function in JavaScript? function main() {    Hello(); }  function Hello() {   // How do you find out the caller function is 'main'? }   Is there a way to find out the call stack?