Working on this. Have to find a solution. Very new to DE: $$\begin{cases}  2yx'(y)-1=x^2(y) \\  x(y=1)=1 \\  \end{cases} $$ Writing this as: \begin{align} 2y \frac{dx}{dy}-1&amp;=x^2y\\ \frac{1}{x^2}2y\,dx-1&amp;=y\,dy\\ \frac{1}{x^2}\,dx &amp;= 1+y\,dy\\ \int \frac{1}{x^2}\,dx &amp;= \int 1+y\,dy\\ -\frac{1}{x}+C &amp;= \frac{y^2}{2}+y+C \end{align} Is this correct? Feel like I'm just doing algebra, but don't really understand if it's correct. Would love feedback.
Really stuck with this, \begin{cases}  2tx'(t)-1=x^2t \\  x(t=1)=1 \\  \end{cases} I don't understand the variables. What does it mean that $x$ differentiated have $t$ as a function value, like this: $x'(t)$? Don't get it :(
Remove empty elements from an array in Javascript What is the purpose of the 'nobody' user? After I read  I noticed that there is a user account named 'nobody' in my Ubuntu system.   Also I noticed that I can login in this account from terminal using the following command and my password:  sudo su nobody     It doesn't mind me at all, but I want to know what is the purpose of this user? Is it created by default on a fresh install of Ubuntu or is created by installing a particular package? Calculating ratio between "rows" in ArcGIS field calculator I have a problem similar to  but that is for QGIS whereas I have to perform it in ArcGIS. I have to calculate the Ratio between rows (sequentially, i.e., row1/row2, row2/row3 and so on) of a specific field based on the ID field and have to assign the results to a separate field. Here is the code and the error message:  def CalcRatio(ID,Frequency):     vDict = {}     with arcpy.da.SearchCursor(&quot;Test&quot;,['Frequency'],'ID = {}'.format(ID)) as sCur:     for Row in sCur:     vDict[Row[0]]=Row[1] # Dict[id] =Frequency     try: value = ( vDict[1] / vDict[2])     except: value = -1     return value  Message: ERROR 000539: Error running expression: CalcRatio( 1 , 50680) Traceback (most recent call last): File &quot;&lt;expression&gt;&quot;, line 1, in &lt;module&gt; File &quot;&lt;string&gt;&quot;, line 5, in CalcRatio IndexError: tuple index out of range  Here is the data OID Id  Frequency 0   1   50680 1   2   49740 2   3   48620 3   4   48300 4   5   48004 5   6   45600 6   7   44384 7   8   42720 8   9   41890 9   10  39700 10  11  38530 11  12  38207 12  13  38106 13  14  37303 14  15  37205 15  16  36527 16  17  35301 17  18  31674 18  19  28890 19  20  24612 Confidence bands in case of fitting ARIMA in R? What Does it Really Mean to Have Different Kinds of Infinities? I am new to Linux and I have Ubuntu 17.04 64-bit (Budgie).  I cannot open steam. It is updated to latest version. When I open it it pops up but after some time it disappears. When I try to run it from a terminal I get this output:  tar: This does not look like a tar archive xz: (stdin): File format not recognized tar: Child returned status 1 tar: Error is not recoverable: exiting now find: ‘/home/ghazi/.steam/ubuntu12_32/steam-runtime’: No such file or directory I'm hoping someone can help! I recently downloaded a torrent directly onto an external hard drive, (using a 2009 MacBook Pro and 1TB Seagate Expansion portable Drive) somehow during the download the drive was accidentally ejected, since this incident when I plug the drive back in it’s having problems reading.  The drive works fine for about 10 minutes, I can read/copy/paste and access files but then starts to wreak havoc; apps hangs, it hangs the Finder, etc.  I’ve tried repairing it in Disk Utility, which reads and repairs this disk but problems inevitably continue as described above.  I’ve deleted the Torrent file also. All my files on this external drive so re-formatting is not an option until I can retrieve them. Is it possible to open directories as administrator? I want to have a root privileges on some directories. How can I do this? Why doesn't the T-800 run? I just re-watched the first two films in the Terminator series. The T1000 (Robert Patrick) does a lot of running, and is quite fast.  I didn't see many scenes where the T800 (Arnie) ran. Is it because he's really heavy? Is he mainly designed as a heavy "stand your ground" machine?  The only scene I could see him running is in T2 in the mental hostpital where the T1000 morphs through the metal gate and his gun gets caught. Then the T800 does a little jog to get into the elevator following John and Sarah. (anybody know of any other running/jogging scenes?) (EDIT Arnie also breaks into a run while pursuing Reece and Sarah down the alley after the NOIR nightclub attack.)  If he can at least jog though, why wouldn't he do this throughout the entire film? You would think that from a "chance of survival" point of view, if he could get a John even the slightest bit faster then he'd do so.  Of course, maybe I am overthinking this... Arnie walking around slowly is a lot more badass than Arnie jogging around.  Edit: Just watched T3 again, the T800 also ran towards the end when the big hangar door was closing and he ran over to slow it down. Interested in other examples of the T800 running too. a 2d planet in the center, where the players will be able to walk on it and also will be affected by center gravity. planet will be static and there won't be any other planets. so;  Is there a way that I can change the gravity position? yes you can adjust gravity via project settings but I want it to be in the middle x,y,z(0,0,0)  I have tried creating my own gravity but it wasn't very useful because objects wouldnt fall, stand on foot and also in contact with another object they would vibrate instead of standing still. (if they stand on the planet they would vibrate)          private void FixedUpdate() {     foreach(GameObject item in grav)     {         Attact(item);     } }  private void Attact(GameObject gmf) {     Rigidbody2D rgg = gmf.GetComponent&lt;Rigidbody2D&gt;();      Vector3 direction = rg2d.position - rgg.position;     float distance = direction.sqrMagnitude;      float forceMag = (10 * rgg.mass) / distance;     Vector3 force = direction.normalized * forceMag * 10;      rgg.AddForce(force); }   I can create a script that will change the gravity by the opposite of the object's position. this does work but I cannot see any way to do it for more than one object. In my online brokerage account, I want to buy a particular stock and I see the following:  Bid:  13.20 x200           Ask:  13.27 x1,000   the current stock price is 13.22.   Can someone explain what the bid and ask prices mean relative to the current price?  If I buy 1000 shares, why would I pay more? Installing debian package through Synaptic I want to install a .deb file. After going through various questions, I came across these three options: dpkg, GDebi and Ubuntu Software Center. However, I want to install the. Deb file via Synaptic Package Manager only. Is there any method by which I can install. Deb file as well as all it's dependencies via Synaptic Package Manager? How does faster than light travel violate causality? Let's say I have two planets that are one hundred thousand lightyears away from each other. I and my immortal friend on the other planet want to communicate, with a strong laser and a tachyon communication device.  I record a message on the tachyon communication device and release the message at exactly the same time as I activate the laser, both of which are directed to the other planet which is one hundred thousand lightyears away. Say it is the year 0 for both of us at the time I did this.  If tachyons existed, then the message would arrive to my friend before the photons in the laser. It would arrive, say, a thousand years earlier. From my vantage point, that message will arrive to her at year 99,999; the same would be true for my friend's vantage point. However, she will only see the laser at year 100,000.  So since she got the message at year 99,999, she immediately sends me a reply back going through the same procedure as I did. She records a message and releases it at the same time as the laser. The tachyons will arrive 1,000 years earlier than the laser, so for me, I will receive the message at year 199,998. I will receive the laser, however, at year 199,999.  It seems to me that communication this way does not violate causality. I will still have received the message after I had sent it.   If tachyons truly violated causality, though, I realize it should arrive at year -1 for her, and so she can reply to me at year -2, which would mess me up by year 0 as I will ask her how she knew I was planning on sending her a message before I sent it. I could send her a different message, which she would end up receiving at year -1, and will end up confusing her as she would have received one message asking her out, and the other asking her how did she know I was asking her out. She then decides I am crazy and sends me a message at year -2 that she does not want to date me, and so she will have both turned me down and entertained me before I have even asked her out.  On the other hand, let's go back to year 0 and add a third device to our list: an Alcubierre drive. After I send out the message and the laser, I get impatient and do not feel like waiting 99,999 years, so I get on my Alcubierre drive spaceship and arrive on her planet at the same year 0. My friend is not in her office, so I leave a note to her also immortal secretary saying I dropped by and that she should expect a message for her in year 99,999.  I then get back on my Alcubierre drive and land back on my planet, still on year 0. Meanwhile, the tachyons and photons I sent out are still racing to arrive to her. By year 99,999, she receives the message just as I Alcubierre drive back to her, and I pick her up for dinner.  But the point of my question is, it seems to me that just going faster than light, if that alone was what you had, would not violate causality. It must be something else. I understand time dilation and that things with mass cannot travel at the speed of light, but using the Alcubierre drive, hypothetically speaking, I was still able to outpace the photons while also having mass. It still did not produce causality problems. Alcubierre drives are also valid solutions to GR.  It seems circular to me to say that what makes traveling faster than light violate causality is because it violates causality (if faster than light communication was divorced from causality problems, then the causality problem would cause itself -- thereby violating causality and, hence, we would scrap it and conclude that there is no causality problem after all).  What is it that I am missing? If someone could help me out, that would be excellent. I've been itching to ask my friend out for a few millenia now. :) I am designing a poster, which has some geometrical shapes (TikZ paths) surrounded by some text. I would like the text to flow neatly around these shapes. I bet there's some clever TikZ magic that could do this.  EDIT: This is the sort of effect I want, sorry to not be clear:    \documentclass[a4paper]{article} \usepackage{tikz} \begin{document} \begin{tikzpicture} \draw (0,0) to (2,-2) to (2,-4) to (4,-4) to [out=up, in=down] (6.5,0); \node [text width=6cm, anchor=north west] at (0,0) { \hspace{5pt}  This is the sort of effect I want to \\ \hspace{23pt} achieve, with text automatically \\ \hspace{36pt} constrained by some \\ \hspace{46pt} geometrical form. Here \\ \hspace{55pt} it's just a curve, \\ \hspace{57pt} but this could \\ \hspace{57pt} also be the \\ \hspace{57pt} text label \\ \hspace{57pt} of a node.}; \end{tikzpicture} \end{document} How to cheat and avoid cheating in Flash games? What is the difference between CentOS "DVD" vs "Everything" ISOs The "Hurry up, it's raid night" achievement in Starcraft 2 involves "beating Wings of Liberty, on normal, in 8 hours or less."  Is there a recommended mission path to take? Which mission should I take for the branching paths? Does it count time spent on the Hyperion in between missions, or is it exclusively time elapsed on missions. Does replaying a mission affect the time? General tips / hints from those who've unlocked the achievement?  Edit: Just got this achievement tonight, finally! The answer was perfect. How to disk copy with unreadable sectors? I want to clone a whole disk bytewise, something like  dd if=/dev/$SRC of=/dev/$DST bs=65536 count=$count   There are better tools for the job, which understand the file system (Windows) and work faster (I don't care), but they fail because of unreadable sectors on the old source disk.  There's actually a single invalid block I have to skip. So I thought about using dd multiple times like  dd if=/dev/$SRC of=/dev/$DST bs=65536 count=... dd if=/dev/zero of=/dev/$DST bs=65536 count=... skip=... seek=... dd if=/dev/$SRC of=/dev/$DST bs=65536 count=... skip=... seek=...   with replacing the broken sector data by zeros. Is this a valid approach? I found this  which confuses me. What are the differences between executing shell scripts using "source file.sh", "./file.sh", "sh file.sh", ". ./file.sh"? We have in and out degree of a directed graph G. if G does not includes loop (edge from one vertex to itself) and does not include multiple edge (from each vertex to another vertex at most one directed edge), we want to check for how many of the following we have a corresponding graph. the vertex number start from 1 to n and the degree sequence are sort by vertex numbers.  a) $d_{in}=(0,1,2,3), d_{out}=(2,2,1,1)$  b) $d_{in}=(2,2,1), d_{out}=(2,2,1)$  c) $d_{in}=(1,1,2,3,3), d_{out}=(2,2,3, 1,2)$  I want to find a nice way instead of drawing graph.  for (C):