What happens if LEDs do not get enough current?
Choosing power supply, how to get the voltage and current ratings?
Getting a random object from NSArray without duplication I am trying to grab the capital letters of a couple of words and wrap them in span tags. I am using  for extract and wrapping purposes, but it's not outputting anything.  preg_replace("/[A-Z]/", "&lt;span class=\"initial\"&gt;$1&lt;/span&gt;", $str) Mysql Pivot rows into dynamic columns with unknown number of columns I have an output of a query as follows:  bid  | code | amount        | ----------------------------- 2915 | BF   |   -10700.00   | 2915 | YQ   |   -300.00     | 2915 | YR   |   0.00        | 2915 | YM   |   0.00        | 2915 | WO   |   -153.00     | 2915 | IN   |   -329.00     | 2915 | K3   |   0.00        | 2915 | CUTE |   -50.00      | -----------------------------   I need to convert the values in code column to individual columns with column name as corresponding code and amount shall be the value.  bid  | BF       | YQ     | ... | CUTE  | ---------------------------------------- 2915 | -10700.00| -300.00| ... | -50.00|   The issue is that the result of my initial query has dynamic codes and hence need to generate columns accordingly.  Already tried the following logic but couldn't achieve the goal:   , ,   All the above links use some expression or the other to generate the columns.   My original resulting rows are result of simple select on multiple joined tables, and has no calculation or expression scope.  Kindly suggest some pointer or hint on how to achieve this.  Many thanks in advance. Let $\mathbb{R^{ n×n}}$ be the space of n × n real matrices. Show that if $ A(t) \in \mathbb{R ^{n×n}}$ is a differentiable function of $t$ then $\frac{d(det A(t))}{dt}$ is the sum of the determinants of $n$ matrices, in which the $i$th matrix is $A(t)$ except that the $i$th row is differentiated. Use this result to prove that the directional derivative of the determinant function at the matrix $A \in \mathbb{R ^{n×n}}$ along the direction $B \in \mathbb{R^{ n×n}}$ is given by $$(det)^{'} (A; B) = tr(Adj(A)B) = \langle Adj(A)^{T} , B \rangle $$ where $Adj(A)$ is the adjoint of $A$, and where the inner product on $\mathbb{R^{n×n}}$ is the trace inner product given by $\langle X, Y \rangle = tr(X^{T} Y )$ Conclude that $$D(det)(A) = Adj(A) ^T $$. $$\lim_{n\to\infty} (1+\frac{2}{n})^{n^2} e^{-2n} = ? $$         $e$   $e^2$   $e^{-1}$   $e^{-2}$      My answer is 1. Since $$\lim_{n \to \infty} \left(1+\frac{2}{n}\right)^{n} =e^{+2}.$$  Therefore $$\lim_{n\to\infty} \left(1+\frac{2}{n}\right)^{n^2} =e^{2n}.$$  Where am I wrong? What is the correct way to pluralize an initialism in which the final word is not pluralized by adding the letter "s"? How can one change an entire document to use bold font? When you have a link from lets say twitter that is t.co/foo that links back to your website how does that effect SEO and how do the major search engines handle Shortened URLs? 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. I had a look at Knuth's The Art of Computer Programming, book 1. In chapter 1, section 1.2.2, exercise 25, he presents the following algorithm for calculating logarithm:  given $x\in[1,2)$, do the following:  L1: [Initialize] Set $y\leftarrow0$, $z\leftarrow x/2$, $k\leftarrow1$.  L2: [Test for end] If $x=1$, stop.  L3: [Compare] If $x-z&lt;1$, go to L5.  L4: [Reduce values] Set $x\leftarrow x-z$, $z\leftarrow x/2^k$, $y\leftarrow y+\log_b(2^k/(2^k-1))$, and go to L2.  L5: [Shift] Set $z\leftarrow z/2$, $k\leftarrow k+1$, and go to L2.  (The algorithm needs an auxiliary table which stores $\log_b2$, $\log_b(4/3)$, and so on, to as many values as the precision of the computer.  Then Knuth concludes: this exercise is to explain why the above algorithm will terminate and why it computes an approximation of $y=\log_b x$.  Well, I see that it works, but I am not able to explain why... What are review tests (audits) and how do they work? I'm quite confused about the following regular expressions I found in a shell script:  ${0##*/} ${0%/*}   How do they work? "None is" or "none are" How can I do a full shutdown of windows 10 without logging in? Let's say a 10N cube (in air, on Earth) rests flat on a scale at the bottom of a tank of water, and the scale reads 8N, so there is 2N of buoyant force on the cube.  How does the buoyant force manifest itself on the cube?  I assume the force is normal to the surface of the scale, but if there isn't any water under the cube, how does the water push up on the cube? How to keep VLC player in minimized mode? I'm using VLC media player which can play almost all kinds of audio and video formats. While listening to audio, I keep VLC in minimized mode and can work on other windows. But when I select to listen video songs mixing with audio songs, VLC is maximizing itself to play every video song in the playing list, which is really annoying in the middle of work.  So how can I keep always VLC player in minimized mode while playing a list of songs mixed with audio and video songs? What are the valid characters for macro names? What is the difference between POST and PUT in HTTP? According to , POST is used to create a resource:  The POST method is used to request that the origin server accept the entity enclosed in the request as a new subordinate of the resource identified by the Request-URI in the Request-Line.  According to , PUT is used to create or replace a resource:  The PUT method requests that the enclosed entity be stored under the supplied Request-URI. If the Request-URI refers to an already existing resource, the enclosed entity SHOULD be considered as a modified version of the one residing on the origin server. If the Request-URI does not point to an existing resource, and that URI is capable of being defined as a new resource by the requesting user agent, the origin server can create the resource with that URI.  So which HTTP method should be used to create a resource? Or should both be supported? Replace \n by a newline in sed portably Why aliases in a non-interactive Bash shell do not work