How would it be possible to copy all new contents from one directory to another so that only new files are copied from the source directory (both directories have the same naming tree). For example, here is the layout of directory A:  /dirA      a.php      b.txt      subdirA1/               readme.txt               config               source_file1.c  /dirB      c.php      subdirA1/               readme.txt   at the end dirB should have all the new files in dirA. Assume that there are only new files in dirA and its sub directories. The result should be the union of the two directories:  /dirB      a.php      b.txt      c.php      subdirA1/               readme.txt               config                                 source_file1.c   I have tried using cp -ra:  cp -ra dirA/* dirB/   but dirB is completely overwritten by dirA.
How do I copy an entire directory into a directory of the same name without replacing the content in the destination directory? (instead, I would like to add to the contents of the destination folder)
On my fully updated Ubuntu 18.04.3 system, audio doesn't work unless I switch between outputs. When I boot my PC, the right output (stereo speakers) is already selected by default, but there is no audio from Chromium, Firefox, VLC or any other program. However, the GNOME speakers test works. I can hear "front left" and "front right" from there, but no audio from other programs. In order to fix that, I can simply switch to another audio output (e.g. HDMI out) and then switch back to the stereo speakers, and the audio will magically work. Any idea why? It's not a big deal because it takes a couple of seconds to switch between outputs, but it's kind of annoying to do that after every reboot. What is a use case where one would use an SObject as a Map key? Run a command without making me wait Proving that the set of limit points of a set is closed $2 \times 2 $ Orthogonal Group I am trying to prove that $O(2)$ has two connected components. This is what I have done: Suppose $A \in O(2)$. Then $A^tA=I$, where $A^t$ is the transpose of $A$ and $I$ is the identity. Taking the determinant of both sides of this equation, we get $\det(A^t)\det(A) = (det(A))^2$   which implies $\det(A) = \pm 1$.  And since $\det$ is continuous (which means that the inverse image of an open set is open), we have $O(2)$ is the disjoint union of $O^+(2)$ and $O^-(2)$. Is this right? Would this be sufficient or would this only prove that there are at least two components? How come SG-1 couldn't get back to Earth? US doctor working in Tripoli wants me to open online account Word meaning the reverse of 'Xenophobia' Xenophobia refers to the irrational fear or hatred of foreigners. But recently I've seen people displaying (in newspaper articles and other places) an irrational fear or hatred of their own countrymen. Is there a word for that? Derivation of survival copula $$ \begin{align}F(x,y) &amp;= P(X\leq x, Y\leq y) \\  &amp;= C(F(x), F(y)) \end{align}$$ The copula of a bivariate distribution is equal to its CDF, $C(u,v) = F(x,y)$. The density of the data's CDF therefore can be expressed as $$f(x,y) = c(u,v) \times f_X(x) f_Y(y)$$ where $c(u,v)$ is the copula density and $f_X(x)$ is a marginal. If $\hat{C}(u,v)$ is the survival copula for determining $$ \begin{align}\bar{F}(x,y) &amp;= P(X&gt; x, Y &gt; y) \\  &amp;= \hat{C}(1-F(x), 1-F(y)) \end{align}$$ how is the first equation of the ordinary copula, $C(u,v)$, linked to the survival copula as $$\hat{C}(u,v) = u + v - 1 + C(1-u,1-v)$$ are $u$ and $v$ merely vectors containing the (ranked) observations of the uniform marginals? A derivation in integrals and probabilities (rather than $F$s) would be good. Let $C$ be the coefficient of $x^2$ in the expansion of the product $(1 - x)(1 + 2x)(1 - 3x)\cdots(1 + 14x)(1 - 15x).$ Find $|C|.$   Just to begin,  $(1-x)(1+2x) = -2x^2 + x + 1$  $(1-x)(1+2x)(1-3x) = 6x^3 - 5x^2 - 2x + 1$   But expanding on like this take too long.  In the end the terms will be like:  $(1 - 15x)(a_0 + a_1x^1 + a_2x^2 + ....)$  Then just looking at the $x^2$, it will be:  $(a_2x^2 - 15a_1x^2) = x^2(a_2 - 15a_1)$  But it it still a very hard problem, any hints? Plot draws list of curves in same color when not using Evaluate Splitting of prime ideals in algebraic extensions I'm reading Algebraic Number Theory by Jurgen Neukirch. I have some problems with some of the exercises in Section 9 of Chapter 1.  They are:  1) If $L / K$ is a Galois extension of algebraic number fields with non-cyclic Galois group, then there are at most finitely many non-split prime ideals of $K$.  2) Let $L / K$ be a finite (not necessarily Galois) extension of algebraic number fields and $N / K$ the normal closure of $L / K$. Show that a prime ideal $p$ of $K$ is totally split in $L$ if and only if it is totally split in $N$.  I have worked on them for a long time but couldn't get any idea of it.   Can you please help? Thank you! What are the limits on how I can cast, change, and retract votes? What limits are there on how I can vote?  How often can I vote? How do my votes become locked/unlocked? I have this problem I'm working on. Hints are much appreciated (I don't want complete proof):  In a normed vector space, if $ x_n \longrightarrow x $ then  $ z_n = \frac{x_1 + \dots +x_n}{n} \longrightarrow x $   I've been trying adding and subtracting inside the norm... but I don't seem to get anywhere.  Thanks! Voltage at soldering iron tip, should I be worried? I discovered that my soldering iron has voltage at the tip and it seems to increase the hotter the iron gets. Should I be worried? I've been trying to repair an old CRT monitor and I'm worried the issues I've been having are due to this cheap iron damaging something.  How to meassure voltage of an soldering iron tip? Where to put probes? Prove $a^\alpha b^{1-\alpha} \le \alpha a + (1 - \alpha)b, \; a,b > 0,\; 0 < \alpha < 1$ Where can I find examples of good Mathematica programming practice? Does an Enlarge/Reduce spell on a druid affect the beast form if the druid Wild-Shapes? If a druid (multiclassed into sorcerer) casts Enlarge on himself so that he becomes a Large humanoid (approximately twelve feet tall), and he then Wild Shapes in a brown bear, is the brown bear form normal size or doubled in all dimensions? What is the word that means “that which can be fixed up at home”?   For example, I buy parts from a store, bring the parts home, and then can construct the thing out of those parts by myself. What is the word that means such an object, one that can be made at home in a do-it-yourself style? I'm trying to identify a novel about an alien race coming to Earth. They are rabbit-like.    I thought it was Niven or Pournell but I cannot remember the title.  It was Quotzal or something like that.