I can't seem to know how to concatenate two char pointer strings using strcat, is it not correct?
Why do I get a segmentation fault when writing to a "char *s" initialized with a string literal, but not "char s[]"?
Access NSMutableArray from another class - Objective C I had a Minecraft world on Minefold.  I archived my Minecraft world just before Minefold closed about a year ago.  I'm trying now to open the world in my local Minecraft installation on OS X, but it doesn't show up in the worlds list.  To import it, I simply unzipped the archive from Minefold into my ~/Library/Application Support/minecraft/saves folder.  I'm running Minecraft 1.8, and I don't have any mods installed.  There's no error; the world just doesn't show up in my list of worlds after I click [Singleplayer] (or [Multiplayer]).  Now, the big clue is that the directory structures are different between my locally-created worlds and the world created on Minefold, but I can't figure out how to adapt the files to make them match:  This is a screenshot of my saves folder. I've circled in blue "local" and "minefold", which contain data files for the local and Minefold worlds, respectively.    I bracketed similar filenames in both worlds, but I'm flummoxed in that the Minefold version has three (3) sets of data files, whereas the local world has only one (1) set of files (even though I have visited Nether in the local world).  How do I load my old Minefold world locally? I cast  on my opponent, whose hand has two Mountain cards. Wistful Thinking resolves and my opponent draws a  and another Mountain.  Can my opponent cast Shock before discarding it? How to merge two files in corresponding row? Now,I have two files:  aaaa.txt:  a=0; b=1; c=2;   bbbb.txt:  d=3 e=4 f=5   I want to merge aaaa.txt and bbbb.txt to cccc.txt.   cccc.txt as follow:  a=0;d=3 b=1;e=4 c=2;f=5   So, what can I do for this? How can I do this fast?  Sure I can do this:  static bool ByteArrayCompare(byte[] a1, byte[] a2) {     if (a1.Length != a2.Length)         return false;      for (int i=0; i&lt;a1.Length; i++)         if (a1[i]!=a2[i])             return false;      return true; }   But I'm looking for either a  function or some highly optimized proven way to do this.  java.util.Arrays.equals((sbyte[])(Array)a1, (sbyte[])(Array)a2);   works nicely, but it doesn't look like that would work for x64.  Note my super-fast answer . DeleteDuplicates[] does not work as expected on floating point values This was a question my friend found in a book.  A block attached to a spring pulled by a constant horizontal force is kept on a smooth horizontal surface. Initially the spring is in its natural state. Then the maximum work that the applied force F can do is:  (a) $F^2/k$ (b) $2F^2/k$ (c) $4F^2/k$ (d) $F^2/2k$  My friend thought that the answer is (a) since the maximum displacement is $x=F/k$ and $W=Fx=F^2/k$. But he saw that the book's answer is different and he asked this question to me. I at first thought that the answer will be (a), but then I realised that this situation is somewhat similar to a charging capacitor. The final energy of the spring is actually $\frac12kx^2=F^2/2k$. So probably the answer is (d)? But the work done is still (a)? But the book says neither. It's (b). This is the logic in the book:  Method 1: in the book:  $$Fx=\frac12kx^2$$  $$x=2F/k$$  $$W=\frac12kx^2=2F^2/k$$  (since the book is an objective questions book it did not have detailed explanations)  What is wrong in the following methods?  Method 2: by calculating the maximum displacement  $$x=F/k$$  $$W=Fx=F^2/k.$$ Method 3: by calculating the final energy  $$x=F/k$$  $$\frac12kx^2=F^2/2k$$  PS: We both know calculus so don't hesitate to use it in the answers. How does "curved space" explain gravitational attraction? They say that gravity is technically not a real force and that it's caused by objects traveling a straight path through curved space, and that space becomes curved by mass, giving the illusion of a force of gravity.  That makes perfect sense for planetary orbits, but a lot less sense for the expression of gravity that we are the most familiar with in our day-to-day lives: "what goes up must come down."  Imagine that I hold a ball in my hand, several feet off the ground, with my fingers curled around it, and my hand is above the ball.  Then I open my fingers, releasing my grip on it, being very careful to not impart any momentum to the ball from my hand as I do so.  An object at rest remains at rest unless acted upon by an outside force.  If the ball is not moving (relative to my inertial reference frame), it has no path to travel that's any different from the Earth's path through space.  It should remain at rest, hanging there in the air.  And yet it falls, demonstrating that an outside force (gravity) did indeed act upon it.  How does curved space explain this? Estimating Uniform distribution endpoints using data with errors Suppose I have a random variable $X$ ~ $Unif(0,\theta)$ where I want to estimate $\theta$. I draw a sample $X_1,...,X_n$.One way is to get a point estimate using e.g.  maximum likelihood estimation via the sufficient statistic $X_{(n)}$.  However, suppose I want a 95% confidence interval of sorts on the value of $\theta$, how should I construct one?  The reason why I am interested in confidence interval is because of the following issue, which is actually my main question (the above prelude on confidence interval is just a suggestion on possible approach). So actually my sample came with some noise, in a sense that I actually observe $X_1+E_1,...,X_n+E_n$ where $E_i$~$N(0,\sigma_i^2)$ independently from each other and from the $X$'s. How should I make some form of statistical estimation about $\theta$? I would prefer some form of confidence estimate. Seeking appropriate statistic to measure spatial autocorrelation of points with binary values I am trying to determine the level of spatial autocorrelation in a point dataset.  The attribute I'm interested in is binary (presence/absence of a species), for which Moran's I is not appropriate.  On the other hand, Joint Count statistics, which are typically recommended for binary or categorical data, apparently are not appropriate for point data. What is an appropriate statistic to measure global and/or local spatial autocorrelation of points when the attribute of interest is binary? Film in which people can time-travel to relive the biggest world disasters; main character changes a destiny, saving many people I saw a film about 10 years ago. It was about people that could live the biggest disasters in the world that had happened again. They could travel in time and see these disasters. There were some plane crashes, metro crashes, Titanic disaster and so on.  But one man (positive main role) saw another bad man who was throwing a coin in the air and this coin fell down. This positive role changed a destiny and saved many people. This saving caused some damages to negative roles in this film. Polygon intersection using turf js I have given this code for intersection: function intersectPolyByPolyFC(poly,fcPoly){         var fgp=[];//variable for feature group         var bbPoly=turf.bboxPolygon(turf.bbox(poly));//polygon representation of the bounding box of a reference polygon         for(var i=0;i&lt;fcPoly.features.length;i++){//loop through the feature collection of polygons             var bb=turf.bboxPolygon(turf.bbox(fcPoly.features[i]));//variable bb represents each polygon for feature collection             if(turf.intersect(bbPoly,bb)){//condition to check if the two bounding boxes intersect                 var int= turf.intersect(poly,fcPoly.features[i]);                 if(int){                     int.properties=fcPoly.features[i].properties;                     fgp.push(int);                 }             }         }         return turf.featureCollection(fgp);     }  and the function definition I have given as var bufline=turf.buffer(line,0.05,{units:&quot;kilometers&quot;}); var intBUOWL= intersectPolyByPolyFC(bufline, lyrBUOWL.toGeoJSON()); L.geoJSON(intBUOWL,{style:{color:'red',weight:5}}).addTo(mymap);  When I am drawing a line over a polygon for intersection I am getting this error Uncaught TypeError: Cannot read property 'map' of undefined     at Object.t.collect (turf.min.js:1)     at summarizePointsByLine (buffer.html:440)     at NewClass.&lt;anonymous&gt; (buffer.html:155)     at NewClass.fire (Events.js:190)     at NewClass._fireCreatedEvent (leaflet.draw.js:8)     at NewClass._fireCreatedEvent (leaflet.draw.js:8)     at NewClass.completeShape (leaflet.draw.js:8)     at HTMLAnchorElement.handler (DomEvent.js:92)  How can I resolve this error? $$A=\begin{array}{ccc} 0 &amp; 1/2 &amp; 0 &amp; \cdots &amp; 0 \\ 1/2 &amp; 0 &amp; 1/2 &amp;\cdots&amp; 0\\ 0 &amp; 1/2 &amp; 0 &amp; \cdots &amp; 0\\ \vdots &amp; \vdots &amp; \vdots &amp;\ddots &amp; 1/2\\ 0 &amp; 0 &amp; 0 &amp; 1/2 &amp; 0 \end{array}$$  I need to know the spectral radius of $A$ in function of the dimension of the matrix $n$. I know only one way to know the spectral radius, using the definition I find all eigenvalues and then find the maximum. but it very hard if $n$ is changing. Some help please!  I did some iteration by   $$det(\lambda I-A)$$  $$n=2 \quad r=\frac{\sqrt{1}}{2}$$ $$n=3 \quad r=\frac{\sqrt{2}}{2}$$  for $n=2$ and $n=3$ are correct.  and if we take this rule, for   $$n=5\quad \quad r=\frac{\sqrt{4}}{2}$$  but this isn´t true since I know radius for this matrix should be $&lt; 1$ and if we take this rule  for $n=5$ we have  $$\frac{\sqrt4}{2}=1$$   Some hint? $a^m=b^m$ and $a^n=b^n$ imply $a=b$ Let $D$ be an integral domain and let $a^m=b^m$ and $a^n=b^n$ where $m$ and $n$ are relatively prime integers, $a,b \in D$.   How do I show $a=b$? Sum of reciprocals of numbers with certain terms omitted I know that the harmonic series $1 + \frac12 + \frac13 + \frac14 + \cdots$ diverges. I also know that the sum of the inverse of prime numbers $\frac12 + \frac13 + \frac15 + \frac17 + \frac1{11} + \cdots$ diverges too, even if really slowly since it's $O(\log \log n)$.  But I think I read that if we consider the numbers whose decimal representation does not have a certain digit (say, 7) and sum the inverse of these numbers, the sum is finite (usually between 19 and 20, it depends from the missing digit). Does anybody know the result, and some way to prove that the sum is finite? Suppose I want a strong 20-bit blockcipher.  In other words, I want a function that takes a key (suppose the key is 128 bits), and implements a permutation from 20 bits to 20 bits.  The set of permutations should be close to a randomly-chosen subset of size $2^{128}$ of all $2^{20}!$ permutations on 20 bits.  I don't want you to build a new blockcipher from scratch.  Instead, assume you have a "strong" blockcipher like AES (128-bit blocksize, 128-bit keysize) and use this to build your 20-bit cipher.   Of course, your construction should be practical (i.e., you should be able to run it in both directions with reasonable amounts of time and memory). How can I get a shapefile from a postgis query? My data is in a PostGIS database. I would like to generate a shapefile from a query. How can I do that? Similar to  on the bugs in Minecraft, I would like a complete list of what error codes exist in Minecraft and how they occur, as well as how they can be resolved. Is there a correct gender-neutral singular pronoun ("his" vs. "her" vs. "their")? Is there a pronoun I can use as a gender-neutral pronoun when referring back to a singular noun phrase?  Each student should save his questions until the end. Each student should save her questions until the end. I have two examples of different scenarios that are confusing to me.  First, if I have a 1/1 creature with first strike and deathtouch, and my opponent blocks it with a 2/2 creature, will my creature die? I can see two alternative ways this could play out and I'm not sure which is correct.   My creature deals his first strike damage, immediately killing the opponent's creature before he is able to deal combat damage as a state-based effect. My creature deals his first strike damage, which would normally be lethal due to deathtouch, but state-based effects are not checked, and thus the opposing creature deals his damage and both die.   I'm almost positive in this case that it's the first option above.  What gets trickier is, for example, if a creature has first strike and a triggered ability "Whenever this creature deals combat damage to a creature, return that creature to its owner's hand."  This is not a state-based effect, but rather uses the stack. Similar to above, there are two possibilities.   My creature deals his first strike damage, and his triggered ability is placed on the stack. The stack waits to resolve until after all combat damage is dealt, so the opposing creature still kills mine. My creature deals his first strike damage, and his triggered ability is placed on the stack. Both players now gain priority between first strike and combat damage (which I don't think normally happens, thus my confusion). The stack finishes resolving, and the opponent's creature doesn't have a chance to deal damage.   Can someone clarify this area of the rules?