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  • Explanation of contribute_to_class

    - by anon.
    I'm attempted to extend code, and have come across an issue, I don't understand a line of code. I know the outcome of it - but I don't understand how it happens and am naturally enough scared to change it. The line of code I've come across is this: MyGenericRelation().contribute_to_class(model, 'field_name') The result of this code is a field with 'field_name' is added to the 'model' and from what I gather the objects inside the field are a list of type X (part of MyGenericRelation). I'm wondering if anyone can explain how this works. As in, why do I get a list of X objects attached to 'field_name' and if does it have to be generic relations prior to contribute_to_class or would using an actual model type, say 'Y' just give me a list of Y's. To be honest, I am more interested in the affect and functionality of the contribute_to_class method.

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  • Dijkstra's Algorithm explanation java

    - by alchemey89
    Hi, I have found an implementation for dijkstras algorithm on the internet and was wondering if someone could help me understand how the code works. Many thanks private int nr_points=0; private int[][]Cost; private int []mask; private void dijkstraTSP() { if(nr_points==0)return; //algorithm=new String("Dijkstra"); nod1=new Vector(); nod2=new Vector(); weight=new Vector(); mask=new int[nr_points]; //initialise mask with zeros (mask[x]=1 means the vertex is marked as used) for(int i=0;i<nr_points;i++)mask[i]=0; //Dijkstra: int []dd=new int[nr_points]; int []pre=new int[nr_points]; int []path=new int[nr_points+1]; int init_vert=0,pos_in_path=0,new_vert=0; //initialise the vectors for(int i=0;i<nr_points;i++) { dd[i]=Cost[init_vert][i]; pre[i]=init_vert; path[i]=-1; } pre[init_vert]=0; path[0]=init_vert; pos_in_path++; mask[init_vert]=1; for(int k=0;k<nr_points-1;k++) { //find min. cost in dd for(int j=0;j<nr_points;j++) if(dd[j]!=0 && mask[j]==0){new_vert=j; break;} for(int j=0;j<nr_points;j++) if(dd[j]<dd[new_vert] && mask[j]==0 && dd[j]!=0)new_vert=j; mask[new_vert]=1; path[pos_in_path]=new_vert; pos_in_path++; for(int j=0;j<nr_points;j++) { if(mask[j]==0) { if(dd[j]>dd[new_vert]+Cost[new_vert][j]) { dd[j]=dd[new_vert]+Cost[new_vert][j]; } } } } //Close the cycle path[nr_points]=init_vert; //Save the solution in 3 vectors (for graphical purposes) for(int i=0;i<nr_points;i++) { nod1.addElement(path[i]); nod2.addElement(path[i+1]); weight.addElement(Cost[path[i]][path[i+1]]); } }

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  • Need an explanation on this code - c#

    - by ltech
    I am getting familiar with C# day by day and I came across this piece of code public static void CopyStreamToStream( Stream source, Stream destination, Action<Stream,Stream,Exception> completed) { byte[] buffer = new byte[0x1000]; AsyncOperation asyncOp = AsyncOperationManager.CreateOperation(null); Action<Exception> done = e => { if (completed != null) asyncOp.Post(delegate { completed(source, destination, e); }, null); }; AsyncCallback rc = null; rc = readResult => { try { int read = source.EndRead(readResult); if (read > 0) { destination.BeginWrite(buffer, 0, read, writeResult => { try { destination.EndWrite(writeResult); source.BeginRead( buffer, 0, buffer.Length, rc, null); } catch (Exception exc) { done(exc); } }, null); } else done(null); } catch (Exception exc) { done(exc); } }; source.BeginRead(buffer, 0, buffer.Length, rc, null); } From this article Article What I fail to follow is that how does the delegate get notified that the copy is done? Say after the copy is done I want to perform an operation on the copied file.

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  • Explanation of `self` usage during dealloc?

    - by Greg
    I'm trying to lock down my understanding of proper memory management within Objective-C. I've gotten into the habit of explicitly declaring self.myProperty rather than just myProperty because I was encountering occasional scenarios where a property would not be set to the reference that I intended. Now, I'm reading Apple documentation on releasing IBOutlets, and they say that all outlets should be set to nil during dealloc. So, I put this in place as follows and experienced crashes as a result: - (void)dealloc { [self.dataModel close]; [self.dataModel release], self.dataModel = nil; [super dealloc]; } So, I tried taking out the "self" references, like so: - (void)dealloc { [dataModel close]; [dataModel release], dataModel = nil; [super dealloc]; } This second system seems to work as expected. However, it has me a bit confused. Why would self cause a crash in that case, when I thought self was a fairly benign reference more used as a formality than anything else? Also, if self is not appropriate in this case, then I have to ask: when should you include self references, and when should you not?

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  • Syntax explanation

    - by Knowing me knowing you
    In code: struct tagPaint { }Paint,//<<<--------------what's this (Paint)? *pPaint;//<<<-------------and this(*pPaint)? I mean do I declare variable with name Paint of type tagPaint and pointer called pPaint to tagPaint? Thanks.

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  • Explanation needed for sum of prime below n numbers

    - by Bala Krishnan
    Today I solved a problem given in Project Euler its problem no 10 and it took 7 hrs for my python program to show the result. But in that forum itself a person named lassevk posted solution for this and it took only 4 sec. And its not possible for me to post this question in that forum because its not discussion forum. So, think about this if you want to mark this question as non-constructive. marked = [0] * 2000000 value = 3 s = 2 while value < 2000000: if marked[value] == 0: s += value i = value while i < 2000000: marked[i] = 1 i += value value += 2 print s If any one understand this code please explain it simple as possible. Link to the Problem 10 question.

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  • setDelegate explanation

    - by mac
    Hi i am new to iphone developement , can any one explain me , why setDelegate is used, where we should use it. [request setDelegate:sender]; thanks in advance.

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  • Correlation formula explanation needed d3.js

    - by divakar
    function getCorrelation(xArray, yArray) { alert(xArray); alert(yArray); function sum(m, v) {return m + v;} function sumSquares(m, v) {return m + v * v;} function filterNaN(m, v, i) {isNaN(v) ? null : m.push(i); return m;} // clean the data (because we know that some values are missing) var xNaN = _.reduce(xArray, filterNaN , []); var yNaN = _.reduce(yArray, filterNaN , []); var include = _.intersection(xNaN, yNaN); var fX = _.map(include, function(d) {return xArray[d];}); var fY = _.map(include, function(d) {return yArray[d];}); var sumX = _.reduce(fX, sum, 0); var sumY = _.reduce(fY, sum, 0); var sumX2 = _.reduce(fX, sumSquares, 0); var sumY2 = _.reduce(fY, sumSquares, 0); var sumXY = _.reduce(fX, function(m, v, i) {return m + v * fY[i];}, 0); var n = fX.length; var ntor = ( ( sumXY ) - ( sumX * sumY / n) ); var dtorX = sumX2 - ( sumX * sumX / n); var dtorY = sumY2 - ( sumY * sumY / n); var r = ntor / (Math.sqrt( dtorX * dtorY )); // Pearson ( http://www.stat.wmich.edu/s216/book/node122.html ) var m = ntor / dtorX; // y = mx + b var b = ( sumY - m * sumX ) / n; // console.log(r, m, b); return {r: r, m: m, b: b}; } I have finding correlation between the points i plot using this function which is not written by me. my xarray=[120,110,130,132,120,118,134,105,120,0,0,0,0,137,125,120,127,120,160,120,148] yarray=[80,70,70,80,70,62,69,70,70,62,90,42,80,72,0,0,0,0,78,82,68,60,58,82,60,76,86,82,70] I can t able to understand the function perfectly. Can anybody explain it with the data i pasted here. I also wanted to remove the zeros getting calculated from this function.

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  • HTML5 - Need explanation about outline

    - by RhymeGuy
    So, lets say that I have the following structure: <doctype html> <header> <h1>Header</h1> <article><h2>Article</h2></article> <article><h2>Article</h2></article> </header> <main> <h1>Main content</h1> <article><h2>Article</h2></article> <article><h2>Article</h2></article> <article><h2>Article</h2></article> <article><h2>Article</h2></article> </main> <section> <h1>Sidebar</h1> </section> If i check outline using http://gsnedders.html5.org/outliner/ (or any other), I'll get outline like this: 1. Main content 1. Header 1. Article 2. Article 2. Article 3. Article 4. Article 5. Article 6. Sidebar Which (from my understanding) is not correct. I have thought that it should look like this: 1. Header 1. Article 2. Article 2. Main content 1. Article 2. Article 3. Article 4. Article 3. Sidebar Why this happens? I can get desired outline if I use section element. But id there is main element in HTML structure, then everything breaks (at least for me - it's not how I understood it). Can I achieve desired outline using main element?

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  • Explanation of output

    - by Anon
    My program class Building { Building() { System.out.print("b "); } Building(String name) { this(); System.out.print("bn " + name); } }; public class House extends Building { House() { System.out.print("h "); // this is line# 1 } House(String name) { this(); // This is line#2 System.out.print("hn " + name); } public static void main(String[] args) { new House("x "); } } We know that compiler will write a call to super() as the first line in the child class's constructor. Therefore should not the output be: b (call from compiler written call to super(), before line#2 b (again from compiler written call to super(),before line#1 ) h hn x But the output is b h hn x Why is that?

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  • Understanding Clojure concurrency example

    - by dusha
    Hello, I just go through various documentation on Clojure concurrency and came accross the example on the website (http://clojure.org/concurrent_programming). (import '(java.util.concurrent Executors)) (defn test-stm [nitems nthreads niters] (let [refs (map ref (replicate nitems 0)) pool (Executors/newFixedThreadPool nthreads) tasks (map (fn [t] (fn [] (dotimes [n niters] (dosync (doseq [r refs] (alter r + 1 t)))))) (range nthreads))] (doseq [future (.invokeAll pool tasks)] (.get future)) (.shutdown pool) (map deref refs))) I understand what it does and how it works, but I don't get why the second anonymous function fn[] is needed? Many thanks, dusha. P.S. Without this second fn [] I get NullPointerException.

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  • C++ streams question (explanation of comment in code)

    - by skyeagle
    I am playing around with the fastCGI application found here. The following comment is in the code: if (content) delete []content; // If the output streambufs had non-zero bufsizes and // were constructed outside of the accept loop (i.e. // their destructor won't be called here), they would // have to be flushed here. My knowledge of C++ streams is rather weak. Could someone please explain the following: which streambufs are being referred to in the comment? under what conditions would the streambufs had non-zero bufsizes? last but not the least, can someone point to a resource (pun intended) online that provides a clear but gentle introduction to C++ IO streams?

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  • Need some explanation about MS Ajax using PageMethods

    - by Ahmed Said
    I have a project that uses PageMethods to call functions on the server. The server functions (written in C#) return the values as array of strings, without doing any kind of serialization and in the client side (from Js) the accessing of the return values is by using static variable called arguments. I found that sometimes for some users (cases are not repro) sometimes an exception occured "WebServiceFailedException the server method 'Foo' returned invalid data. the 'd' property is missing from JSON." Some searching on google I found that people are serializing the return values using DataContractJsonSerializer class and in js accessing the return value using one of the callback function Example: function OnRequestComplete(result, userContext, methodName) { var Person = eval('(' + result + ')'); alert(Person.Forename); alert(Person.Surname); } So is the first technique is correct? or what?

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  • Brief Explanation of C Supersets?

    - by Ben Hooper
    I'm getting more and more confused in regards to C's supersets the further I venture into the programming world. There's just so many versions.. C, C++, C#, Objective-C, Objective-C++ and God knows what else. I only know tidbits about these languages (some are object-oriented, some are procedural, C was originally developed for UNIX, C++ started as an extension and is used primarily on the Windows OS, Objective-C is primarily used on Linux and Mac OS/iOS, etc), but I'm not even sure that what I know is correct. I would just like someone to shed some light on what I "know" - a little bit more information about which are successive versions, which platforms each are generally used on, which are the best versions to learn, etc if anyone is feeling generous. :) Thanks. :)

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  • need explanation about bookmarking

    - by Sachindra
    I got stumbled upon this issue once and I guess I need some expertise in getting through this .." some links that one likes to bookmark ." I tried browsing and got confused. is bookmarking just means the use of CTRL + D. Or is ti something like the one in this link .

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  • OpenGL Pixel Format Attributes (NSOpenGLPixelFormatAttibutes) explanation?

    - by nacho4d
    Hi, I am not new to OpenGL, but not an expert. Many tutorials teach how to draw, 3D, 2D, projections, orthogonal, etc, but How about setting a the view? (NSOpenGLView in Cocoa, Macs). For example I have this: - (id) initWithFrame: (NSRect) frame { GLuint attribs[] = { //PF: PixelAttibutes NSOpenGLPFANoRecovery, NSOpenGLPFAWindow, NSOpenGLPFAAccelerated, NSOpenGLPFADoubleBuffer, NSOpenGLPFAColorSize, 24, NSOpenGLPFAAlphaSize, 8, NSOpenGLPFADepthSize, 24, NSOpenGLPFAStencilSize, 8, NSOpenGLPFAAccumSize, 0, 0 }; NSOpenGLPixelFormat* fmt = [[NSOpenGLPixelFormat alloc] initWithAttributes: (NSOpenGLPixelFormatAttribute*) attribs]; return self = [super initWithFrame:frame pixelFormat: [fmt autorelease]]; } And I don't understand very well their usage, specially when combining them. For example: If I want my view to be capable of full screen should I write NSOpenGLPFAFullScreen only ? or both? (by capable I mean not always in full screen) Regarding Double Buffer, what is this exactly? (Below: Apple's definition) If present, this attribute indicates that only double-buffered pixel formats are considered. Otherwise, only single-buffered pixel formats are considered Regarding Color: if NSOpenGLPFAColorSize is 24 and NSOpenGLPFAColorSize is 8 then it means that alpha and RGB components are treated differently? what happen if I set the former to 32 and the later to 0? Etc, etc,In general how do I learn to set my view from scratch? Thanks in advance. Ignacio.

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  • What is the explanation for "warning: assuming that the loop is not infinite"

    - by James Morris
    I had just taken the decision to change as many variables from unsigned to int and upon recompiling the code in question, was greeted by this warning message: freespace_state.c:203: warning: assuming that the loop is not infinite The line in question: for (x = startx; x <= endx; ++x, ++xptr) This loop is 60 lines of code (inc white space/brackets etc), and has a goto within it, and at least one occurrence of continue. In this case, I think I am appreciative that GCC is assuming this loop is not infinite, because, it should never loop indefinitely. What is GCC trying to tell me here?

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  • PHP while(variable=mysql_fetch_assoc) - explanation

    - by Petr
    Hi, I have been working with C# so this is quite strange for me: while($variable=mysql_fetch_assoc) I have not been able to look up in PHP manual how it works. I guess that in each loop it advances to next element of assoc.array. But what is this generally called in PHP? I am just not used to see '=' in loop condition.

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  • Can anybody tell me exactly what the Object doesn't support this property or method means in IE for

    - by helle
    Hey guys, while surfing through the web and through stackoverflow.com i found many posts in forums, etc. where this message occures in IE but not in the other browsers. the thing is, the resolutions vary widely and it's not clear for me what's the best way to avoid this problem. So my question is, if anybody knows exactly, specificly what this message Object doesn't support this property or method means, causes, says ,... thanks for help. helle

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  • Need Explanation of couchdb reduce function

    - by Alan
    From http://wiki.apache.org/couchdb/Introduction_to_CouchDB_views The couchdb reduce function is defined as function (key, values, rereduce) { return sum(values); } key will be an array whose elements are arrays of the form [key,id] values will be an array of the values emitted for the respective elements in keys i.e. reduce([ [key1,id1], [key2,id2], [key3,id3] ], [value1,value2,value3], false) I am having trouble understanding when/why the array of keys would contain different key values. If the array of keys does contain different key values, how would I deal with it? As an example, assume that my database contains movements between accounts of the form. {"amount":100, "CreditAccount":"account_number", "DebitAccount":"account_number"} I want a view that gives the balance of an account. My map function does: emit( doc.CreditAccount, doc.amount ) emit( doc.DebitAccount, -doc.amount ) My reduce function does: return sum(values); I seem to get the expected results, however I can't reconcile this with the possibility that my reduce function gets different key values. Is my reduce function supposed to group key values first? What kind of result would I return in that case?

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  • An explanation of memory usage on Windows server 2003

    - by Rich
    Hi, We've been working on a bit of puzzle at work. We have an application service installed on two machines, both running Windows server 2003. These services do exactly the same thing. However once loaded, one of the services uses 200mb less than the other service. We're at a bit of a loss to what might be causing this discrepancy. I was wondering if there was some kind of server setting that would cause an application to use more memory (heap block size) or anything to explain this. If anyone has any ideas on what may be causing this, or how to find out what is causing this I'd be very grateful. Cheers Rich

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