Ubuntu 20.04 Wifi Option Non-existant (No GNOME, No option in settings)
Wi-Fi not working on Lenovo ThinkPad E570 (Realtek RTL8821CE)
I've been writing C and C++ code for almost twenty years, but there's one aspect of these languages that I've never really understood. I've obviously used regular casts i.e.  MyClass *m = (MyClass *)ptr;   all over the place, but there seem to be two other types of casts, and I don't know the difference. What's the difference between the following lines of code?  MyClass *m = (MyClass *)ptr; MyClass *m = static_cast&lt;MyClass *&gt;(ptr); MyClass *m = dynamic_cast&lt;MyClass *&gt;(ptr); When do you use at the office? And when do you use in the office? What's the difference between the phrases? We know the escape velocity from the Earth is 11.2km/s. Isn't it the velocity required to escape from earth if we go normal to the surface of earth? i.e while we derive the formula for the escape velocity from earth we never consider the slanted motion of the object. So when we launch a rocket we need to use very less value of velocity compare to escape velocity to escape from earth because rocket follows a slanted path so curvature of earth has an effect?  If what I said above is right, then how we can say escape velocity is 11.2 km/s? Using restroom on airplane while fasten seatbelt light is on? This question about  over on  made me wonder what a passenger is supposed to do when they urgently have to use the restroom while the fasten seat belt light is on. FAA regulations require passengers to obey the seat-belt sign, even if flight attendants do not.  I saw this happen on a flight where an older gentleman asked the flight attendant if he could use the restroom, and she said "not until the light is off". The flight had been free of turbulence for 15 minutes or so by this time, and the flight attendants were walking freely throughout the cabin, collecting post-meal trash, etc. The gentleman who asked to use the restroom appeared to be in quite some discomfort, and practically ran to the restroom when the light went off 10 minutes later.  So what is a passenger supposed to do when he isn't permitted to use the lavatory, when he has to go and can't wait? Just go in their seat? I'm running a VPS of a german provider and want to switch from Ubuntu to CentOS. There I tried to install firewalld (was not preinstalled), but it always fails with the error  ERROR: Failed to load nf_conntrack module: modprobe: ERROR: could not find module by name='nf_conntrack' modprobe: ERROR: could not insert 'nf_conntrack': Function not implemented modprobe: ERROR: Error running install command for nf_conntrack modprobe: ERROR: could not insert 'nf_conntrack': Operation not permitted   Obviously the nf_conntrack kernel module was not found. Since this is a VPS, I cannot tinker with the kernel modules. On the support site of my provider I found a list of available kernel modules, for example:  ip_conntrack_netbios_ns ipt_conntrack    ip_conntrack    ip_conntrack_ftp    ip_conntrack_irc   Since nf_conntrack is not listed here, does that mean, that I cannot use firewalld? Is it possible to run it without this module?  I guess I could use iptables, if I wanted to (it seems to run correctly). But as I have more experience with firewalld, I would like to stick with it.    CentOS Linux release 7.7.1908 (Core)  uname -a: Linux xxxxxx.xxxxxxxx.xxx 3.10.0-042stab140.1 #1 SMP Thu Aug 15 13:32:22 MSK 2019 x86_64 x86_64 x86_64 GNU/Linux I am trying to find all 1- or 2- dimensional Lie Algebras "a" up to isomorphism. This is what I have so far:  If a is 1-dimensional, then every vector (and therefore every tangent vector field) is of the form $cX$. Then , by anti-symmetry, and bilinearity:  $$[X,cX]=c[X,X]= -c[X,X]==0$$  I think this forces a unique Lie algebra because Lie algebra isomorphisms preserve the bracket.  I also know Reals $\mathbb{R}$ are the only 1-dimensional Lie group, so its Lie algebra ($\mathbb{R}$ also) is also 1-dimensional. How can I show that every other 1-dimensional algebra is isomorphic to this one? Do I use preservation of bracket?  For 2 dimensions, I am trying to use the fact that the dimension of the Lie algebra g of a group $G$ is the same as the dimension of the ambient group/manifold $G$. I know that all surfaces (i.e., groups of dimension 2) can be classified as products of spheres and Tori, and I think the only 2-dimensional Lie group is $S^1\times S^1$, but I am not sure every Lie algebra can be realized as the Lie algebra of a Lie group ( I think this is true in the finite-dimensional case, but I am not sure).  I know there is a result out there that I cannot yet prove that all 1- and  2-dimensional Lie algebras are isomorphic to Lie subalgebras of $GL(2,\mathbb{R})$ (using matrix multiplication, of course); would someone suggest how to show this last? Thanks. Why disable Fast Boot on Windows 8 when having dual booting? Why is everybody keep mentioning to disable Fast Boot on Windows 8 if you have installed alongside Ubuntu? Is it something that is recommended only for UEFI machines or is it a suggestion for Legacy BIOS machines as well? Is it because it makes the Windows partition inaccessible from Linux or there is another more serious reason to disable it? How to define a bijection between $(0,1)$ and $(0,1]$? How to define a bijection between $(0,1)$ and $(0,1]$?   Or any other open and closed intervals?   If the intervals are both open like $(-1,2)\text{ and }(-5,4)$ I do a cheap trick (don't know if that's how you're supposed to do it): I make a function $f : (-1, 2)\rightarrow (-5, 4)$ of the form $f(x)=mx+b$ by \begin{align*} -5 = f(-1) &amp;= m(-1)+b \\ 4 = f(2) &amp;= m(2) + b \end{align*} Solving for $m$ and $b$ I find $m=3\text{ and }b=-2$ so then $f(x)=3x-2.$  Then I show that $f$ is a bijection by showing that it is injective and surjective. How can I put the computer to sleep from Command Prompt/Run menu? How do I rollback a TFS check-in? I'd like to rollback a change I made recently in TFS. In Subversion, this was pretty straightforward.  However, it seems to be an incredible headache in TFS: Option 1: Get Prior Version  Manually get prior version of each file Check out for edit Fail - the checkout (in VS2008) forces me to get the latest version  Option 2: Get TFS Power Tools  Download Team Foundation Power Tools Issue rollback command from cmd line Fail - it won't work if there are any other pending changes  Option 3: Manually Undo Changes  manually undo my changes, then commit a new changeset  Question How do I rollback to a previous changeset in TFS? Using principal component analysis (PCA) for feature selection Does walking fast prevent eggs hatching? I have a couple of eggs that I've picked up from some Pokestops (I'm lucky enough to live above one).   I walk a lot. I get to work through a 2 mile walk / train journey every day, so I should be picking up loads of steps for the eggs I have. However, because I'm normally always running late... for everything, I have to rush everywhere, so I walk at an above average pace.   Today I've walked around 5 miles, but the game has registered 100 metres. Is this because I walk too fast, or because of something else?  It's worth pointing out that I have the app open when walking... mostly because I have to catch them all. (This made me miss a train this morning... luckily I was early :D) How to parse HTML with PHP? How to set static IP address? I have configured network adapter of guest Ubuntu to work in a bridged mode so I could ssh to it from the host machine.   The problem is that the guest Ubuntu ip address keep changing.   Even though it changes  within a very short range 192.168.0.4-10 it is still takes time to configure Putty and other programs each time.  Is there a way to make the guest Ubuntu ip address to be static?  My guest OS has the full GUI. Best practices for making a WordPress site "movable"? I'm planning to buy a domain and install a WordPress site on it at a web-hosting company.  But first I'll need to iron-out some bugs...  I got a working LAMP-stack at my home-computer, so I'm thinking about first installing my site locally - off the Internet.  I'll be mostly tweaking and making "test-posts" to check that everything works, but I'll probably also make some posts I'd like to keep when I move the site and take it online.  When I'm done chasing bugs; I guess I'll just package the public_html|www directory-tree and upload it to the web-hosting company, and also export the database from my home-computer to the web-hosting.    What I'm wondering if there are some "best practices", some do-s and don't-s, some major pits to take note of?    For example, how can ensure the smooth transition of domain-name in posts and links as such, from localhost to whatever-i-end-up-buying.com (I know from previous attempt of running WordPress at my home computer, that this didn't always work quite well...). What is the difference between parseInt() and Number()? Can the Universe be deterministic and still allow free will? Is there a way for non-root processes to bind to "privileged" ports on Linux? It's very annoying to have this limitation on my development box, when there won't ever be any users other than me.  I'm aware of , but none of them do exactly what I want:    (The version in Debian testing, 1.0, only supports IPv4)  (the "nat" table is not yet implemented for ip6tables, the IPv6 version of iptables) sudo (Running as root is what I'm trying to avoid) SELinux (or similar). (This is just my dev box, I don't want to introduce a lot of extra complexity.)   Is there some simple sysctl variable to allow non-root processes to bind to "privileged" ports (ports less than 1024) on Linux, or am I just out of luck?  EDIT: In some cases, you can  to do this. How to put a framed box around text + math environment Prove $\sum\limits_{i=2}^{n}\frac{1}{(i-1)i}$ = $\frac{(n-1)}{n}$ using induction. I need to prove $\sum\limits_{i=2}^{n}\frac{1}{(i-1)i}$ = $\frac{(n-1)}{n}$ using induction. I am getting stuck midway through the inductive step.   Here is what I have:  $\forall n\geq 2$, where $n\in\mathbb{N}, P(n)$ is the statement "$\sum\limits_{i=2}^{n}\frac{1}{(i-1)i}$ = $\frac{(n-1)}{n}$".  Base case:  $\sum\limits_{i=2}^{2}\frac{1}{(i-1)i}$ = $\frac{1}{2}$ = $\frac{(2-1)}{2}$ so $P(2)$ is true.  Inductive assumption: Assume $P(n)$ is true. Need to show $\sum\limits_{i=2}^{n+1}\frac{1}{(i-1)i}$ = $\frac{((n+1)-1)}{(n+1)}$.  $\sum\limits_{i=2}^{n}\frac{1}{(i-1)i}$ + $\frac{1}{n^{2}}$ = $\frac{(n-1)}{n}$ + $\frac{1}{n^{2}}$  = $\frac{n(n-1) + 1}{n^{2}}$ = $\frac{n^{2}-n+1}{n^{2}}$  I got stuck here and tried working backward from $\frac{((n+1)-1)}{(n+1)}$, which gives me:  $\frac{((n+1)-1)}{(n+1)}$ = $\frac{n}{(n+1)}$   Any suggestions on what to do next or where I may be going wrong?