Differences in meaning between present perfect and present perfect continuous
Is there any difference between Present Perfect and Present Perfect Continuous?
Detecting pattern at the end of a line with grep Why is the sum of two random variables a convolution? For long time I did not understand why the "sum" of two random variables is , whereas a mixture density function sum of $f(x)$ and $g(x)$ is $p\,f(x)+(1-p)g(x)$; the arithmetic sum and not their convolution. The exact phrase "the sum of two random variables" appears in google 146,000 times, and is elliptical as follows. If one considers an RV to yield a single value, then that single value can be added to another RV single value, which has nothing to do with convolution, at least not directly, all that is is a sum of two numbers. An RV outcome in statistics is however a collection of values and thus a more exact phrase would be something like "the set of coordinated sums of pairs of associated individual values from two RV's is their discrete convolution"...and can be approximated by the convolution of the density functions corresponding to those RV's. Even simpler language: 2 RV's of $n$-samples are in effect two n-dimensional vectors that add as their vector sum.           Please show the details of how the sum of two random variables are a convolution and a sum. Find $f$ if $ f(x)+f\left(\frac{1}{1-x}\right)=x $ Find $f$ if $$ f(x)+f\left(\frac{1}{1-x}\right)=x $$ I think, that I have to find x that $f(x) = f\left(\frac{1}{1-x}\right)$ I've tried to put x which make $x = \frac{1}{1 - x}$, but this equation has no roots in real numbers. Does there exist a surjective homomorphism from $(\mathbb R,+)$ to $(\mathbb Q,+)$ ? Does there exist a surjective homomorphism from $(\mathbb R,+)$ to $(\mathbb Q,+)$ ?  ( I know that there 'is' a   'surjection' , but I don't know whether any surjective homomrophism from $\mathbb R$ to $\mathbb Q$ exist or not . Please help . Thanks in advance ) Will the Windows 10 Free Upgrade stay in the Professional channel? Qualcomm Atheros AR9462 with Ubuntu 18.10 I can't enable the Wifi (nothing happens when press enable button) and in Wifi settings it says:     "No Wi-Fi Adapter Found"   I have tried several things from other questions/answers here but nothing worked. Here some information if this is helpful for the answer:     Device: Lenovo Miix 2 11   sudo lspci:  Network controller: Qualcomm Atheros AR9462 Wireless Network Adapter (rev 01)   sudo lshw -C network:  *-network DISABLED            description: Wireless interface    product: AR9462 Wireless Network Adapter    vendor: Qualcomm Atheros    physical id: 0    bus info: pci@0000:02:00.0    logical name: wlp2s0    version: 01    serial: 48:d2:24:8a:ea:e6    width: 64 bits    clock: 33MHz    capabilities: pm msi pciexpress bus_master cap_list rom ethernet physical wireless    configuration: broadcast=yes driver=ath9k driverversion=4.18.0-16-generic firmware=N/A latency=0 link=no multicast=yes wireless=IEEE 802.11    resources: irq:18 memory:f0400000-f047ffff memory:f0480000-f048ffff   sudo lsmod | grep ath:  ath3k                  20480  0 bluetooth             548864  12 btrtl,btintel,btbcm,bnep,ath3k,btusb ath9k                 151552  0 ath9k_common           36864  1 ath9k ath9k_hw              475136  2 ath9k_common,ath9k ath                    36864  3 ath9k_common,ath9k,ath9k_hw mac80211              794624  1 ath9k cfg80211              663552  5 wl,ath9k_common,ath9k,ath,mac80211   In system settings it shows the Wifi-Adapter Name:  Qualcomm Atheros AR9462   Edit:  lspci -knn | grep Net -A3; rfkill list:  02:00.0 Network controller [0280]: Qualcomm Atheros AR9462 Wireless Network Adapter [168c:0034] (rev 01) Subsystem: Lenovo AR9462 Wireless Network Adapter [17aa:3214] Kernel driver in use: ath9k Kernel modules: ath9k, wl 0: phy0: Wireless LAN     Soft blocked: no     Hard blocked: no 1: ideapad_wlan: Wireless LAN     Soft blocked: no     Hard blocked: yes 2: ideapad_bluetooth: Bluetooth     Soft blocked: yes     Hard blocked: yes How should I act when I see tiny "Have you tried this..?" type of answers? I would like to achieve this effect using my Nikon P510:      Are there any suggestions or tips that would help me do that? Based on the question , I got curious. Is there a guide or resource that describes how the price of a ticket is determined?  When you search you often see curious effects like cheaper tickets for a flight from A to B with a layover compared to a direct flight. This seems counter-intuitive from an outsider's perspective since you fly twice. Also one way tickets more expensive than 2 ways.  It can be a short set of rules. Something that helps someone to get started with finding good prices. I know these can be very complex and they probably change over time and over airline interests but there is probably a simplified set of rules that can be enunciated. Is it possible to link multiple leaders lines to one piece of annotation?  I'm working in ArcGIS 10.2 Desktop Advanced with non-feature linked geodatabase annotation. I have hundreds of numbers labeling various polygons, but some polygons share a number. Instead of creating multiple numbers/annotations for each polygon I'd like to have one number with multiple lines pointing to each polygon.   So, in the image below, the number 5 corresponds to multiple polygons. Here I've moved 5 from it's ideal location to show that the second leader line is not connected to the number annotation. My workaround has been to create another piece of geodatabase annotation with a blank text string to serve as a placeholder for a leader line. The other option was to use map/graphic annotation to create the second leader line, but with the multiple disadvantages of not being in the same annotation feature class as the number annotation.    My goal would be for each piece of number annotation to be connected to multiple leader lines like appears below. How to execute code after html form reset with jquery? Piping data through arbitrary functions in Clojure What was Stack Exchange 1.0? I've seen a few users mention that certain SE sites like  and  are unique, as they were originally created as Stack Exchange 1.0 sites.  As a fairly recent user, I don't know what Stack Exchange 1.0 was like. The current version of Stack Exchange is the only version I've ever known.   What was Stack Exchange 1.0? What changed between SE 1.0 and 2.0? How to cook a pork sirloin roast? I picked up a pork sirloin roast yesterday, it's a little over three pounds.  I've never cooked one of these before and I am not sure what to do.  My seasoning plan is salt, pepper, thyme, and rosemary, and I might poke a couple holes for cloves of garlic as well.  My cooking plan is 8+ hours in the crock pot on low, with about an inch of water in there.  Will this turn out OK?  I'd like a tender and moist result, obviously.  Any tips would be greatly appreciated. How do I add polygons to fill a face? trying to recreate this Elijah bottle. I have two sides, one of which is outlined in red. How do I fill that face with polygons so I can then grab the center (that red square dot) to pull it outward thereby creating the slight outward bowing of the bottle? How to create a circular shaped grid, similar to a manhole cover Bravo for allowing comment editing, but what's the explanation for enforcing a five-minute window?  I think this might be over-engineering. If I have a spelling mistake or an inaccuracy I'd like to fix, I don't think the fact that five minutes has elapsed should prevent me from fixing it.  Further, if you are worried people will edit their comments in a way that makes the comment thread nonsensical, they can already do this by deleting their comment. So, limiting the ability to edit isn't really helping much in that regard.  Update  If people don't like this idea, I'm definitely open to hearing your reasons. For now, it seems like an unnecessary limitation of a quite awesome feature.  Update 2  Regarding John's scenario...     Me: Obama is cool!   You: You are right, man!      My edit: Obama is an idiot!   You: You are right, man!   ...this problem can still occur with deletions...     user1: Obama is cool!   user2: No, McCain is cool!   you: You are right, man!        user1: Obama is cool!   ---- deleted -----   you: You are right, man!     So, yes, editing could be abused as you suggest, but discontinuities can occur already because of deletions (and as someone else mentioned, because upvoted comments get prioritized upward).  As for Jeff's argument about rate limiting, I agree that is important, but I don't understand why you can't just use a CAPTCHA to prevent too many edits in a short period of time. I got  question in review. First sentence is:     I know there is a  question, but no answers.   And indeed the two questions are virtually identical. I started to flag as duplicate - but the original question had no answer at the time, so it wouldn't be correct and apparently . (I didn't go so far as to try to submit the flag).  What is the proper action here? How do we want such a question to be handled? Should both (or more) questions stay open indefinitely until either is answered and somebody gets the good idea to do the duplicate linking?   As the new question is essentially a bump to the front page (perhaps with re-tagging), especially in the case where the OP knows that a previous question exist, perhaps something should be done to enable bumping re-emphasizing without writing the new question.  As I wrote this,  actually got an answer. So the old one should now be closed as a duplicate of the new - but my question remains for the case where all known/found duplicate questions have no answer?  Ironically, just before asking this, the "Questions that may already have your answer" gave me ... (Although the suggestion has no answer). So it has been asked before - the comment there even suggest the ability to re-emphasize. Is it possible to redirect all of the output of a Bourne shell script to somewhere, but with shell commands inside the script itself? Redirecting the output of a single command is easy, but I want something more like this: #!/bin/sh if [ ! -t 0 ]; then     # redirect all of my output to a file here fi  # rest of script...  Meaning: if the script is run non-interactively (for example, cron), save off the output of everything to a file.  If run interactively from a shell, let the output go to stdout as usual. I want to do this for a script normally run by the FreeBSD periodic utility.  It's part of the daily run, which I don't normally care to see every day in email, so I don't have it sent.  However, if something inside this one particular script fails, that's important to me and I'd like to be able to capture and email the output of this one part of the daily jobs. Update: Joshua's answer is spot-on, but I also wanted to save and restore stdout and stderr around the entire script, which is done like this: # save stdout and stderr to file  # descriptors 3 and 4,  # then redirect them to &quot;foo&quot; exec 3&gt;&amp;1 4&gt;&amp;2 &gt;foo 2&gt;&amp;1  # ...  # restore stdout and stderr exec 1&gt;&amp;3 2&gt;&amp;4 Why is the Earth so fat? I made a naive calculation of the height of Earth's equatorial bulge and found that it should be about 10km.  The true height is about 20km.  My question is: why is there this discrepancy?  The calculation I did was to imagine placing a ball down on the spinning Earth.  Wherever I place it, it shouldn't move.  The gravitational potential per unit mass of the ball is $hg$, with $h$ the height above the pole-to-center distance of the Earth (call that $R$) and $g$ gravitational acceleration.  Gravity wants to pull the ball towards the poles, away from the bulge.  It is balanced by the centrifugal force, which has a potential $-\omega^2R^2\sin^2\theta/2$ per unit mass, with $\omega$ Earth's angular velocity and $\theta$ the angle from the north pole.  This comes taking what in an inertial frame would be the ball's kinetic energy and making it a potential in the accelerating frame.  If the ball doesn't move, this potential must be constant, so  $$U = hg - \frac{(\omega R \sin\theta)^2}{2} = \textrm{const}$$  we might as well let the constant be zero and write  $$h = \frac{(\omega R \sin\theta)^2}{2g}$$  For the Earth,   $$R = 6.4*10^6m$$  $$\omega = \frac{2\pi}{24\ \textrm{hours}}$$  $$g = 9.8\ m/s^2$$  This gives 10.8 km when $\theta = \pi/2$, so the equatorial bulge should be roughly that large.    , the Earth is 42.72 km wider in diameter at the equator than pole-to-pole, meaning the bulge is about twice as large as I expected.  (Wikipedia cites diameter; I estimated radius.)  Where is the extra bulge coming from?  My simple calculation uses $g$ and $R$ as constants, but neither varies more than a percent or so.  It's true the Earth does not have uniform density, but it's not clear to me how this should affect the calculation, so long as the density distribution is still spherically-symmetric (or nearly so).  (Wikipedia also includes , without derivation, that agrees with mine.)