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Testing When Correctness is Poorly Defined?

- by dsimcha

I generally try to use unit tests for any code that has easily defined correct behavior given some reasonably small, well-defined set of inputs. This works quite well for catching bugs, and I do it all the time in my personal library of generic functions. However, a lot of the code I write is data mining code that basically looks for significant patterns in large datasets. Correct behavior in this case is often not well defined and depends on a lot of different inputs in ways that are not easy for a human to predict (i.e. the math can't reasonably be done by hand, which is why I'm using a computer to solve the problem in the first place). These inputs can be very complex, to the point where coming up with a reasonable test case is near impossible. Identifying the edge cases that are worth testing is extremely difficult. Sometimes the algorithm isn't even deterministic. Usually, I do the best I can by using asserts for sanity checks and creating a small toy test case with a known pattern and informally seeing if the answer at least "looks reasonable", without it necessarily being objectively correct. Is there any better way to test these kinds of cases?

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C++ Matrix class hierachy

- by bpw1621

Should a matrix software library have a root class (e.g., MatrixBase) from which more specialized (or more constrained) matrix classes (e.g., SparseMatrix, UpperTriangluarMatrix, etc.) derive? If so, should the derived classes be derived publicly/protectively/privately? If not, should they be composed with a implementation class encapsulating common functionality and be otherwise unrelated? Something else? I was having a conversation about this with a software developer colleague (I am not per se) who mentioned that it is a common programming design mistake to derive a more restricted class from a more general one (e.g., he used the example of how it was not a good idea to derive a Circle class from an Ellipse class as similar to the matrix design issue) even when it is true that a SparseMatrix "IS A" MatrixBase. The interface presented by both the base and derived classes should be the same for basic operations; for specialized operations, a derived class would have additional functionality that might not be possible to implement for an arbitrary MatrixBase object. For example, we can compute the cholesky decomposition only for a PositiveDefiniteMatrix class object; however, multiplication by a scalar should work the same way for both the base and derived classes. Also, even if the underlying data storage implementation differs the operator()(int,int) should work as expected for any type of matrix class. I have started looking at a few open-source matrix libraries and it appears like this is kind of a mixed bag (or maybe I'm looking at a mixed bag of libraries). I am planning on helping out with a refactoring of a math library where this has been a point of contention and I'd like to have opinions (that is unless there really is an objective right answer to this question) as to what design philosophy would be best and what are the pros and cons to any reasonable approach.

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Compilation problem in the standard x86_64 libraries

- by user350282

Hi everyone, I am having trouble compiling a program I have written. I have two different files with the same includes but only one generates the following error when compiled with g++ /usr/lib/gcc/x86_64-linux-gnu/4.4.1/../../../../lib/crt1.o: In function `_start': /build/buildd/eglibc-2.10.1/csu/../sysdeps/x86_64/elf/start.S:109: undefined reference to `main' collect2: ld returned 1 exit status The files I am including in my header are as follows: #include <google/sparse_hash_map> using google::sparse_hash_map; #include <ext/hash_map> #include <math.h> #include <iostream> #include <queue> #include <vector> #include <stack> using std::priority_queue; using std::stack; using std::vector; using __gnu_cxx::hash_map; using __gnu_cxx::hash; using namespace std; Searching the internet for those two lines hasn't resulted in anything to help me. I would be very grateful for any advice. Thank you

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select2: "text is undefined" when getting json using ajax

- by user3046715

I'm having an issue when getting json results back to select2. My json does not return a result that has a "text" field so need to format the result so that select2 accepts "Name". This code works if the text field in the json is set to "text" but in this case, I cannot change the formatting of the json result (code outside my control). $("#e1").select2({ formatNoMatches: function(term) {return term +" does not match any items." }, ajax: { // instead of writing the function to execute the request we use Select2's convenient helper url: "localhost:1111/Items.json", dataType: 'jsonp', cache: true, quietMillis: 200, data: function (term, page) { return { q: term, // search term p: page, s: 15 }; }, results: function (data, page) { // parse the results into the format expected by Select2. var numPages = Math.ceil(data.total / 15); return {results: data.Data, numPages: numPages}; } } }); I have looked into the documentation and found some statements you can put into the results such as text: 'Name', but I am still getting "text is undefined". Thanks for any help.

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How create new array which subtracts values from 2 double arrays in C#?

- by Tomek eM

Helou it's my problem, I have 2 array which have double values: (this is function which get back values(latitude) from richTextBox) private Tuple<double>[] szerokosc(string[] lines) { return Array.ConvertAll(lines, line => { string[] elems = line.Split(','); double we = 0.01 * double.Parse(elems[3], EnglishCulture); int stopnie = (int)we; double minuty = ((we - stopnie) * 100) / 60; double szerokosc_dziesietna = stopnie + minuty; return new Tuple<double>(Math.Round(szerokosc_dziesietna, (int)numericUpDown2.Value)); }); ; } (this part of code call function) var data1 = szerokosc(szerdlugeo_diag_gps.Lines); var data2 = szerokosc(szerdlugeo_diag_gpsglonass.Lines); What should I do, to get something like this: for example: var data3 = data1 - data2; My values in this data looks like (f.e.) data1 = (x11, x12, ... x1(n) ): 53.11818160073043, 53.11816348903661, 53.11814874695463, ... data2 = (x21, x22, ... x(2n) ): 53.11814200771546, 53.118131477652156, 53.11812263239697, 53.11811884157276, 53.11811631435644, .... I would like back data3 = (x31=x11-x21, x32=x12=x22, ... x(3n)=x(1n)-x(2n) ) It would be good if it included the following condition: if data1 = ( 1, 5, 6, 8) data2 = (1.5, 3.3) data3 = (-0.5, 1.7) not data3 = (-0.5, 1.7, 6, 8) Please help.

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Instrumenting a string

- by George Polevoy

Somewhere in C++ era i have crafted a library, which enabled string representation of the computation history. Having a math expression like: TScalar Compute(TScalar a, TScalar b, TScalar c) { return ( a + b ) * c; } I could render it's string representation: r = Compute(VerbalScalar("a", 1), VerbalScalar("b", 2), VerbalScalar("c", 3)); Assert.AreEqual(9, r.Value); Assert.AreEqual("(a+b)*c==(1+2)*3", r.History ); C++ operator overloading allowed for substitution of a simple type with a complex self-tracking entity with an internal tree representation of everything happening with the objects. Now i would like to have the same possibility for NET strings, only instead of variable names i would like to see a stack traces of all the places in code which affected a string. And i want it to work with existing code, and existing compiled assemblies. Also i want all this to hook into visual studio debugger, so i could set a breakpoint, and see everything that happened with a string. Which technology would allow this kind of things? I know it sound like an utopia, but I think visual studio code coverage tools actually do the same kind of job while instrumenting the assemblies.

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Recoverable error while running XSL

- by Kate

XSL: <?xml version="1.0" encoding="utf-8"?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:ve="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math" xmlns:v="urn:schemas-microsoft-com:vml" xmlns:wp="http://schemas.openxmlformats.org/drawingml/2006/wordprocessingDrawing" xmlns:w10="urn:schemas-microsoft-com:office:word" xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main" xmlns:wne="http://schemas.microsoft.com/office/word/2006/wordml" exclude-result-prefixes="wp wne w10 w ve o r m v" version="2.0"> <xsl:output method="text"/> <xsl:param name="styleName"/> <xsl:template match="w:p"> <xsl:apply-templates/><xsl:text>
</xsl:text> </xsl:template> <xsl:template match="w:r[not ((parent::w:hyperlink[@w:anchor[matches(.,concat('^(',$styleName,')')),'i']]))]"> <xsl:value-of select="replace(., '.', '＀')"/> </xsl:template> </xsl:stylesheet> While processing the above XSL, I am getting the below error, Recoverable Error: Recoverable error on line 11 FORG0006: An error occurred matching pattern {w:r[not ((parent::w:hyperlink[@w:anchor[matches(.,concat('^(',$styleName,')')),'i']]))]}: Effective boolean value is not defined for a sequence of two or more items starting with a boolean Please Help. I am not able to figure out this.

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How to proceed jpeg Image file size after read--rotate-write operations in Java?

- by zamska

Im trying to read a JPEG image as BufferedImage, rotate and save it as another jpeg image from file system. But there is a problem : after these operations I cannot proceed same file size. Here the code //read Image BufferedImage img = ImageIO.read(new File(path)); //rotate Image BufferedImage rotatedImage = new BufferedImage(image.getHeight(), image.getWidth(), BufferedImage.TYPE_3BYTE_BGR); Graphics2D g2d = (Graphics2D) rotatedImage.getGraphics(); g2d.rotate(Math.toRadians(PhotoConstants.ROTATE_LEFT)); int height=-rotatedImage.getHeight(null); g2d.drawImage(image, height, 0, null); g2d.dispose(); //Write Image Iterator iter = ImageIO.getImageWritersByFormatName("jpeg"); ImageWriter writer = (ImageWriter)iter.next(); // instantiate an ImageWriteParam object with default compression options ImageWriteParam iwp = writer.getDefaultWriteParam(); try { FileImageOutputStream output = null; iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT); iwp.setCompressionQuality(0.98f); // an integer between 0 and 1 // 1 specifies minimum compression and maximum quality File file = new File(path); output = new FileImageOutputStream(file); writer.setOutput(output); IIOImage iioImage = new IIOImage(image, null, null); writer.write(null, iioImage, iwp); output.flush(); output.close(); writer.dispose(); Is it possible to access compressionQuality parameter of original jpeg image in the beginning. when I set 1 to compression quality, the image gets bigger size. Otherwise I set 0.9 or less the image gets smaller size. How can i proceed the image size after these operations? Thank you,

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C++ Suppress Automatic Initialization and Destruction

- by Travis G

How does one suppress the automatic initialization and destruction of a type? While it is wonderful that T buffer[100] automatically initializes all the elements of buffer, and destroys them when they fall out of scope, this is not the behavior I want. #include <iostream> static int created = 0, destroyed = 0; struct S { S() { ++created; } ~S() { ++destroyed; } }; template <typename T, size_t KCount> class Array { private: T m_buffer[KCount]; public: Array() { // some way to suppress the automatic initialization of m_buffer } ~Array() { // some way to suppress the automatic destruction of m_buffer } }; int main() { { Array<S, 100> arr; } std::cout << "Created:\t" << created << std::endl; std::cout << "Destroyed:\t" << destroyed << std::endl; return 0; } The output of this program is: Created: 100 Destroyed: 100 I would like it to be: Created: 0 Destroyed: 0 My only idea is to make m_buffer some trivially constructed and destructed type like char and then rely on operator[] to wrap the pointer math for me, although this seems like a horribly hacked solution. Another solution would be to use malloc and free, but that gives a level of indirection that I do not want.

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C++ program crashes at runtime

- by qwerty

Hello, I have this simple c++ program #include <cstdlib> #include <iostream> #include <math.h> #include <stdlib.h> #include <time.h> #include <vector> using namespace std; int aleator(int n) { return (rand()%n)+1; } int main() { int r; int indexes[100]={0}; // const int size=100; //int a[size]; std::vector<int>v; srand(time(0)); for (int i=0;i<25;i++) { int index = aleator(100); if (indexes[index] != 0) { // try again i--; continue; } indexes[index] = 1; cout << v[index] ; } cout<<" "<<endl; system("pause"); return 0; } But at runtime it crashes, so i got that error with 'Send error report' and 'Don't send'. What i'm doing wrong? Thanks!

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Which OpenGL functions are not GPU-accelerated?

- by Xavier Ho

I was shocked when I read this (from the OpenGL wiki): glTranslate, glRotate, glScale Are these hardware accelerated? No, there are no known GPUs that execute this. The driver computes the matrix on the CPU and uploads it to the GPU. All the other matrix operations are done on the CPU as well : glPushMatrix, glPopMatrix, glLoadIdentity, glFrustum, glOrtho. This is the reason why these functions are considered deprecated in GL 3.0. You should have your own math library, build your own matrix, upload your matrix to the shader. For a very, very long time I thought most of the OpenGL functions use the GPU to do computation. I'm not sure if this is a common misconception, but after a while of thinking, this makes sense. Old OpenGL functions (2.x and older) are really not suitable for real-world applications, due to too many state switches. This makes me realise that, possibly, many OpenGL functions do not use the GPU at all. So, the question is: Which OpenGL function calls don't use the GPU? I believe knowing the answer to the above question would help me become a better programmer with OpenGL. Please do share some of your insights.

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Decimal To Octal Converter, last digit issue

- by Srishan Supertramp

I tried making a C program to convert a user entered decimal number to octal. I wrote the C code with my own logic without any research of how other users try to do it. It works fine for the number 601 and some other numbers but for most numbers it returns the octal equivalent with the last digit being 1 less than it should be. For 75 it returns 112 instead of 113. I realize using printf with %o gets the job done but it's kind of defeating the purpose of learning to program. Here's my code: #include <stdio.h> #include <math.h> /* converting decimal to octal */ int main() { int n,x,y,p,s; printf("Enter a decimal number "); scanf("%d",&x); s=0;p=0; while (x!=0) { y=x%8; s=s+y*pow(10,p); x=(x-y)/8; p=p+1; } printf("the octal equivalent is: %d\n",s); getch(); return 0; }

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What to call factory-like (java) methods used with immutable objects

- by StaxMan

When creating classes for "immutable objects" immutable meaning that state of instances can not be changed; all fields assigned in constructor) in Java (and similar languages), it is sometimes useful to still allow creation of modified instances. That is, using an instance as base, and creating a new instance that differs by just one property value; other values coming from the base instance. To give a simple example, one could have class like: public class Circle { final double x, y; // location final double radius; public Circle(double x, double y, double r) { this.x = x; this.y = y; this.r = r; } // method for creating a new instance, moved in x-axis by specified amount public Circle withOffset(double deltaX) { return new Circle(x+deltaX, y, radius); } } So: what should method "withOffset" be called? (note: NOT what its name ought to be -- but what is this class of methods called). Technically it is kind of a factory method, but somehow that does not seem quite right to me, since often factories are just given basic properties (and are either static methods, or are not members of the result type but factory type). So I am guessing there should be a better term for such methods. Since these methods can be used to implement "fluent interface", maybe they could be "fluent factory methods"? Better suggestions? EDIT: as suggested by one of answers, java.math.BigDecimal is a good example with its 'add', 'subtract' (etc) methods. Also: I noticed that there's this question (by Jon Skeet no less) that is sort of related (although it asks about specific name for method)

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loop is cut one element of the array

- by Walaa

The problem is : Write a program that reads a number n and then declares an array of n elements. The program then fills the array with the first n numbers, where each number is two to the power of the previous. Finally, display array’s contents. My code : import java.util.*; public class Q1 { static Scanner scan = new Scanner (System.in); public static void main(String args [] ) { int num; int i = 0; System.out.println("Enter a number :"); num = scan.nextInt(); double [] a=new double[num]; a[0]= num ; for ( ;i<=a.length-1 ; i++) { a[i+1] = Math.pow(2,a[i]); System.out.println((int)(a[i]) ); } } } The error is : ----jGRASP exec: java Q1 Enter a number : 4 4 16 65536 Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4 at Q1.main(Q1.java:16) ----jGRASP wedge2: exit code for process is 1. why it says that? And the number by user printed twice!

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Animate screen while loading textures

- by Omega

My RPG-like game has random battles. When the player enters a random battle, it is necessary for my game to load the textures used within that battle (animated monsters, animations, etc). The textures are quite a lot, and rather big (the battles are very graphical intensive). Such process consumes significant time. And while it is loading, the whole screen freezes. The game's map freezes, and the wait time is significant - I personally find it annoying. I can't afford to preload the textures because, after doing some math, I realized: If I preload all the textures at the beginning of the game, the application will definitely crash. If I preload the textures that are used in a specific map when the player enters the map, the application is very likely to crash as well. I can only afford to load the textures when I need them, and dispose of them as soon as the battle ends. I'd prefer to not use a "loading screen" image because it affects my game's design and concept. I want to avoid this approach. If I could do some kind of animation while loading the textures, it would be great, which leads to my question: is that possible? What kind of animation, you ask? Well, how about... you remember when Final Fantasy used to distort the screen while apparently loading the textures? Something like that. But well, distorting is quite a time-consuming process as well, so maybe just a cool frame-by-frame animation or something. While writing this, I realized that I could make small pauses between textures (there are multiple textures), and during such pauses, I update the screen to represent the animation's state. However, this is very unlikely to happen, because each texture is 2048x2048, so the animation would be refreshed at a rather laggy (and annoying) rate. I'd prefer to avoid this as well.

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Project Euler, Problem 10 java solution now working

- by Dennis S

Hi, I'm trying to find the sum of the prime numbers < 2'000'000. This is my solution in java but I can't seem get the correct answer. Please give some input on what could be wrong and general advice on the code is appreciated. Printing 'sum' gives: 1308111344, which is incorrect. /* The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17. Find the sum of all the primes below two million. */ class Helper{ public void run(){ Integer sum = 0; for(int i = 2; i < 2000000; i++){ if(isPrime(i)) sum += i; } System.out.println(sum); } private boolean isPrime(int nr){ if(nr == 2) return true; else if(nr == 1) return false; if(nr % 2 == 0) return false; for(int i = 3; i < Math.sqrt(nr); i += 2){ if(nr % i == 0) return false; } return true; } } class Problem{ public static void main(String[] args){ Helper p = new Helper(); p.run(); } }

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What OpenGL functions are not GPU accelerated?

- by Xavier Ho

I was shocked when I read this (from the OpenGL wiki): glTranslate, glRotate, glScale Are these hardware accelerated? No, there are no known GPUs that execute this. The driver computes the matrix on the CPU and uploads it to the GPU. All the other matrix operations are done on the CPU as well : glPushMatrix, glPopMatrix, glLoadIdentity, glFrustum, glOrtho. This is the reason why these functions are considered deprecated in GL 3.0. You should have your own math library, build your own matrix, upload your matrix to the shader. For a very, very long time I thought most of the OpenGL functions use the GPU to do computation. I'm not sure if this is a common misconception, but after a while of thinking, this makes sense. Old OpenGL functions (2.x and older) are really not suitable for real-world applications, due to too many state switches. This makes me realise that, possibly, many OpenGL functions do not use the GPU at all. So, the question is: Which OpenGL function calls don't use the GPU? I believe knowing the answer to the above question would help me become a better programmer with OpenGL. Please do share some of your insights.

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Problem finding the difference in days between two dates

- by James

I have been using a tidy little routine that I found here to calculate the difference in days between two dates in AS3. I am getting some strange results and I am wondering if any of you inter-codal-mega-lords can shed some light? Why is Q1 of 2010 coming up one day short, when in all other cases the routine is performing fine? Many thanks in advance to anyone who can help! function countDays( startDate:Date, endDate:Date ):int { var oneDay:int = 24*60*60*1000; // hours*minutes*seconds*milliseconds var diffDays:int = Math.abs((startDate.getTime() - endDate.getTime())/(oneDay)); return diffDays; } countDays( new Date( 2010, 00, 01 ), new Date( 2011, 00, 01 ) ); // returns 365, which is correct countDays( new Date( 2010, 00, 01 ), new Date( 2010, 03, 01 ) ); // returns 89, which is 1 day short countDays( new Date( 2010, 03, 01 ), new Date( 2010, 06, 01 ) ); // returns 91, which is correct countDays( new Date( 2010, 06, 01 ), new Date( 2010, 09, 01 ) ); // returns 92, which is correct countDays( new Date( 2010, 09, 01 ), new Date( 2011, 00, 01 ) ); // returns 92, which is correct

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Three most critical programming concepts

- by Todd

I know this has probably been asked in one form or fashion but I wanted to pose it once again within the context of my situation (and probably others here @ SO). I made a career change to Software Engineering some time ago without having an undergrad or grad degree in CS. I've supplemented my undergrad and grad studies in business with programming courses (VB, Java,C, C#) but never performed academic coursework in the other related disciplines (algorithms, design patterns, discrete math, etc.)...just mostly self-study. I know there are several of you who have either performed interviews and/or made hiring decisions. Given recent trends in demand, what would you say are the three most essential Comp Sci concepts that a developer should have a solid grasp of outside of language syntax? For example, I've seen blog posts of the "Absolute minimum X that every programmer must know" variety...that's what I'm looking for. Again if it's truly a redundancy please feel free to close; my feelings won't be hurt. (Closest ones I could find were http://stackoverflow.com/questions/164048/basic-programming-algorithmic-concepts- which was geared towards a true beginner, and http://stackoverflow.com/questions/648595/essential-areas-of-knowledge-which I didn't feel was concrete enough). Thanks in advance all! T.

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Algorithm to pick values from set to match target value?

- by CSharperWithJava

I have a fixed array of constant integer values about 300 items long (Set A). The goal of the algorithm is to pick two numbers (X and Y) from this array that fit several criteria based on input R. Formal requirement: Pick values X and Y from set A such that the expression X*Y/(X+Y) is as close as possible to R. That's all there is to it. I need a simple algorithm that will do that. Additional info: The Set A can be ordered or stored in any way, it will be hard coded eventually. Also, with a little bit of math, it can be shown that the best Y for a given X is the closest value in Set A to the expression X*R/(X-R). Also, X and Y will always be greater than R From this, I get a simple iterative algorithm that works ok: int minX = 100000000; int minY = 100000000; foreach X in A if(X<=R) continue; else Y=X*R/(X-R) Y=FindNearestIn(A, Y);//do search to find closest useable Y value in A if( X*Y/(X+Y) < minX*minY/(minX+minY) ) then minX = X; minY = Y; end end end I'm looking for a slightly more elegant approach than this brute force method. Suggestions?

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How to display buttons after enterframe event is over in Corona?

- by user1463542

I am trying to display two buttons called countd_again and main_menu after my enterframe event is over. I can't see those buttons after enterframe event is over,though. Can you check my code,please? And also i want to add new addListener for the buttons using director and scene. module(..., package.seeall) function new() local localGroup = display.newGroup(); display.setStatusBar(display.HiddenStatusBar) local background = display.newImage("background.png") start=os.time() cnt=1 local countd_again = display.newImage("yeniden.png") countd_again.x=100 countd_again.y=100 countd_again.isVisible= false; countd_again.alpha=0; countd_again.scene="helloWorld"; local main_menu= display.newImage("anamenu.png") main_menu.x=100 main_menu.y=300 main_menu.isVisible=false; main_menu.alpha=0; main_menu.scene="helloWorld" -- listener function local function onEveryFrame( event ) if (cnt~=0) then cnt= 3-(os.time()-start) minute = math.floor(cnt/60) second=cnt%60 --print(minute,second) minTxt=display.newText(minute,50,50,nil,100) secTxt=display.newText(second,250,50,nil,100) transition.to(minTxt, {time=100, alpha=0}) transition.to(secTxt,{time=100, alpha=0}) else Runtime: removeEventListener("enterFrame",onEveryFrame) countd_again.isVisible=true; main_menu.isVisible=true; transition.to(countd_again,{time=500,alpha=1}); transition.to(main_menu,{time=500,alpha=1}); countd_again: addEventListener("touch", changeScene) main_menu: addEventListener("touch", changeScene) end end -- assign the above function as an "enterFrame" listener Runtime:addEventListener( "enterFrame", onEveryFrame ) function changeScene(e) if(e.phase=="ended") then director:changeScene(e.target.scene); end end countd_again: addEventListener("touch", changeScene) main_menu: addEventListener("touch", changeScene) localGroup: insert(countd_again) localGroup:insert(main_menu) localGroup:insert(background) return localGroup; end

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C program - Seg fault, cause of

- by resonant_fractal

Running this gives me a seg fault (gcc filename.c -lm), when i enter 6 (int) as a value. Please help me get my head around this. The intended functionality has not yet been implemented, but I need to know why I'm headed into seg faults already. Thanks! #include<stdio.h> #include<math.h> int main (void) { int l = 5; int n, i, tmp, index; char * s[] = {"Sheldon", "Leonard", "Penny", "Raj", "Howard"}; scanf("%d", &n); //Solve Sigma(Ai*2^(i-1)) = (n - k)/l if (n/l <= 1) printf("%s\n", s[n-1]); else { tmp = n; for (i = 1;;) { tmp = tmp - (l * pow(2,i-1)); if (tmp <= 5) { // printf("Breaking\n"); break; } ++i; } printf("Last index = %d\n", i); // ***NOTE*** //Value lies in next array, therefore ++i; index = tmp + pow(2, n-1); printf("%d\n", index); } return 0; }

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[Ruby] Modifying object inside a loop doesn't change object outside of the loop?

- by Jergason

I am having problems with modifying objects inside blocks and not getting the expected values outside the blocks. This chunk of code is supposed to transform a bunch of points in 3d space, calculate a score (the rmsd or root mean squared deviation), and store both the score and the set of points that produced that score if it is lower than the current lowest score. At the end, I want to print out the best bunch of points. first = get_transformed_points(ARGV[0]) second = get_transformed_points(ARGV[1]) best_rmsd = first.rmsd(second) best_points = second #transform the points around x, y, and z and get the rmsd. If the new points # have a smaller rmsd, store them. ROTATION = 30 #rotate by ROTATION degrees num_rotations = 360/ROTATION radians = ROTATION * (Math::PI/180) num_rotations.times do |i| second = second * x_rotate num_rotations.times do |j| second = second * y_rotate num_rotations.times do |k| second = second * z_rotate rmsd = first.rmsd(second) if rmsd < best_rmsd then best_points = second best_rmsd = rmsd end end end end File.open("#{ARGV[1]}.out", "w") {|f| f.write(best_points.to_s)} I can print out the points that are getting stored inside the block, and they are getting transformed and stored correctly. However, when I write out the points to a file at the end, they are the same as the initial set of points. Somehow the best_points = second chunk doesn't seem to be doing anything outside of the block. It seems like there are some scoping rules that I don't understand here. I had thought that since I declared and defined best_points above, outside of the blocks, that it would be updated inside the blocks. However, it seems that when the blocks end, it somehow reverts back to the original value. Any ideas how to fix this? Is this a problem with blocks specifically?

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Flash AS3: How to Make scroll bar react to dynamic textfield movement?

- by HeroicNate

I've been looking for a tutorial and answer to this for a while but can't find what I'm looking for. I am loading html text into a dynamic textfield, and I have a scrollbar controlling the scroll using the code below. What I want to do is also add scroll up/down buttons and have the scroll bar move in relation to the text scroll. I was just going to use "tracklistingtext.scrollV -- " for the scroll buttons, but right now the scroll bar doesn't recognize the text movement. What do I need to do to get the scroll bar to listen to the text scroll position? var listTextreq:URLRequest=new URLRequest("tracklist.txt"); var listTextLoader:URLLoader = new URLLoader(); var bounds:Rectangle=new Rectangle(scrollMC.x,scrollMC.y,0,300); var scrolling:Boolean=false; function fileLoaded(event:Event):void { tracklistingtext.htmlText=listTextLoader.data; tracklistingtext.multiline=true; tracklistingtext.wordWrap=true; scrollMC.addEventListener(MouseEvent.MOUSE_DOWN, startScroll); stage.addEventListener(MouseEvent.MOUSE_UP, stopScroll); addEventListener (Event.ENTER_FRAME, enterHandler); } listTextLoader.addEventListener(Event.COMPLETE, fileLoaded); listTextLoader.load(listTextreq); function startScroll(e:Event):void { scrolling=true; scrollMC.startDrag(false,bounds); } function stopScroll(e:Event):void { scrolling=false; scrollMC.stopDrag(); } function enterHandler (e:Event):void { if (scrolling == true) { tracklistingtext.scrollV = Math.round(((scrollMC.y - bounds.y)/300)*tracklistingtext.maxScrollV); } } Any help is greatly appreciated.

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JavaScript: why `null == 0` is false?

- by lemonedo

I had to write a routine that increments the value of a variable by 1 if it is a number, or assigns 0 to the variable if it is not a number. The variable can be incremented by the expression, or be assigned null. No other write access to the variable is allowed. So, the variable can be in three states: it is 0, a positive integer, or null. My first implementation was: v >= 0 ? v += 1 : v = 0 (Yes, I admit that v === null ? v = 0 : v += 1 is the exact solution, but I wanted to be concise then.) It failed since null >= 0 is true. I was confused, since if a value is not a number, an numeric expression involving it must be false always. Then I found that null is like 0, since null + 1 == 1, 1 / null == Infinity, Math.pow(2.718281828, null) == 1, ... Strangely enough, however, null == 0 is evaluated to false. I guess null is the only value that makes the following expression false: (v == 0) === (v >= 0 && v <= 0) So why null is so special in JavaScript?

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