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• error in encryption program

  - by Raja

  #include<iostream> #include<math.h> #include<string> using namespace std; int gcd(int n,int m) { if(m<=n && n%m ==0) return m; if(n<m) return gcd(m,n); else return gcd(m,n%m); } int REncryptText(char m) { int p = 11, q = 3; int e = 3; int n = p * q; int phi = (p - 1) * (q - 1); int check1 = gcd(e, p - 1); int check2 = gcd(e, q - 1); int check3 = gcd(e, phi); // // Compute d such that ed = 1 (mod phi) //i.e. compute d = e-1 mod phi = 3-1 mod 20 //i.e. find a value for d such that phi divides (ed-1) //i.e. find d such that 20 divides 3d-1. //Simple testing (d = 1, 2, ...) gives d = 7 // double d = Math.Pow(e, -1) % phi; int d = 7; // public key = (n,e) // (33,3) //private key = (n,d) //(33 ,7) double g = pow(m,e); int ciphertext = g %n; // Now say we want to encrypt the message m = 7, c = me mod n = 73 mod 33 = 343 mod 33 = 13. Hence the ciphertext c = 13. //double decrypt = Math.Pow(ciphertext, d) % n; return ciphertext; } int main() { char plaintext[80],str[80]; cout<<" enter the text you want to encrpt"; cin.get(plaintext,79); int l =strlen(plaintext); for ( int i =0 ; i<l ; i++) { char s = plaintext[i]; str[i]=REncryptText(s); } for ( int i =0 ; i<l ; i++) { cout<<"the encryption of string"<<endl; cout<<str[i]; } return 0; }

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• PHP - Why does my computation produce a different result when I assign it to a variable?

  - by David

  I want to round a number to a specific number of significant digits - basically I want the following function: round(12345.67, 2) -> 12000 round(8888, 3) -> 8890 I have the following, but there's a strange problem. function round_to_sf($number, $sf) { $mostsigplace = floor(log10(abs($number)))+1; $num = $number / pow(10, ($mostsigplace-$sf)); echo ($number / pow(10, ($mostsigplace-$sf))).' '.$num.'<BR>'; } round_to_sf(41918.522, 1); Produces the following output: 4.1918522 -0 How can the result of a computation be different when it's assigned to a variable?

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• Python to C# Conversion of RGBA values not working

  - by clangers

  I'm currently converting some python code to C#, and I'm having an issue with the RGBA C# libraries # Original Python Code: d = math.sqrt( (x - size/2.0)**2 + (y - size/2.0)**2 ) rgbVal = int(200*d/md + 50) rgba = (0,0,0, 255 - rgbVal) img.putpixel((x,y), rgba) // My C# Code double d = Math.Sqrt(Math.Pow((x - DotSize / 2.0), 2) + Math.Pow((y - DotSize / 2.0), 2)); int rgbVal = (int) (200 * d / md + 50); Color color = Color.FromArgb(255 - rgbVal, 0, 0, 0); // ** ERROR ** img.SetPixel(x,y, color); At both instances of the code d is equal to 106 and md is equal to 53. However the resulting rgbVal value is 450. This would obviously mean that 255 - 450 is -195, which causes an error to be thrown as each individual value must be between 0 and 255. Anyone have any idea how I can fix this. Please note that the data is the same when running both the python and C# versions.

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• return type while using GMP.h header file

  - by Raveesh_Kumar

  While i m using gmp.h header file. i need a fuction which takes inputs of type mpz_t and return mpz_t type too. I m very beginner of using gmp.h So, Here is snaps follows of my approached code.... mpz_t sum_upto(mpz_t max) { mpz_t sum; mpz_init(sum); mpz_init(result); for(int i=0;i<=max-1;i++) mpz_add_ui(sum,sum,pow(2,i)); return sum; } but it will show error 1 ." pow has been not used in this scope.",although i have added math.h in very beginnig of the file. 2 . sum_upto declared as function returning an array... do tell as soon as possible. i have to complete my very big project....

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• C Different answers for a variable when running 'Debug' and 'Start without debug'

  - by Craz

  I keep getting this weird output from my code everytime I use the 'start without degugging' (ctrl-F5) as opposed to normal 'debug' (F5). When I try to find the following value of norm_differnece in debug (pressing F5) mode, it gives me the correct answer for norm_difference normdifference = 1.000000 but in 'start without debugging' (pressing ctrl-f5) the wrong output normdifference = 1456816083547664100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.000000 The following is a segment of code which is gives the output Note: X[] = is a array of stored DOUBLE values for(i=0;i<n;i++){ sum_difference += (pow((X[i*n]-X[i]),2)); } norm_difference = sqrt(norm_difference); for(i=0;i<n;i++){ sum_norm_1 += pow(X[i],2); } norm_1 = sqrt(norm_1); //Take square root of the sum of squares for the row printf("normdifference = %f \n norm_1 = %f \n",norm_difference,norm_1);

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• Proper Translation of equation to C#

  - by Shykin

  I am trying to replicate this equation: Slope(b) = (NSXY - (SX)(SY)) / (NSX2 - (SX)2) in C# but I'm getting the following issue: If I make the average of X = 1 + 2 + 3 + 4 + 5 and the average Y = 5 + 4 + 3 + 2 + 1 it gives me a positive slope even though it is clearly counting down. If I place the same numbers into this calculator: http://www.easycalculation.com/statistics/regression.php It gives me a negative slope in the linked calculator with the same data. I'm trying to narrow down the reasons so is the following a proper translation from equation to C# code: Slope(b) = (NSXY - (SX)(SY)) / (NSX2 - (SX)2) to Slope (m) = ((x * avgX * avgY) - (avgX * avgY)) / ((x * Math.Pow(avgX, 2)) - Math.Pow(avgX, 2));

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• CodePlex Daily Summary for Saturday, June 11, 2011

  CodePlex Daily Summary for Saturday, June 11, 2011Popular ReleasesSimplePlanner: v2.0b: For 2011-2012 Sem 1 ???2011-2012 ????Econ NetVert: 2.4.2.14 Production: Many thanks to paulhickman for testing and reporting issues. - this release has lots of bugfixes in codeconversion when using NRefactory 4.0 (local) and VisualStudio Projects conversionVisual Studio 2010 Help Downloader: 1.0.0.3: Domain name support for proxy Cleanup old packages bug Writing to EventLog with UAC enabled bug Small fixes & RefactoringMedia Companion: MC 3.406b weekly: With this version change a movie rebuild is required when first run -else MC will lock up on exit. Extract the entire archive to a folder which has user access rights, eg desktop, documents etc. Refer to the documentation on this site for the Installation & Setup Guide Important! If you find MC not displaying movie data properly, please try a 'movie rebuild' to reload the data from the nfo's into MC's cache. Fixes Movies Readded movie preference to rename invalid or scene nfo's to info ext...SCCM Client Actions Tool: SCCM Client Actions Tool v0.5.1: SCCM Client Actions Tool v0.5.1 is currently the most stable version and includes all of the functionality requested so far. It comes with following changes since last version: Fixed an incorrect path to x64 client setup folder. It comes as a ZIP file that contains three files: ClientActionsTool.hta – The tool itself. Cmdkey.exe – command line tool for managing cached credentials. This is needed for alternate credentials feature when running the HTA on Windows XP. Cmdkey.exe is natively a...Windows Azure VM Assistant: AzureVMAssist V1.0.0.5: AzureVMAssist V1.0.0.5 (Debug) - Test Release VersionSizeOnDisk: 1.8.0.3: Fix (issue 317): Main window icon loading error on windows server 2003 32bit runing on x86 cpu. Bypass of the Microsoft windows comexception.NetOffice - The easiest way to use Office in .NET: NetOffice Release 0.9: Changes: - fix examples (include issue 16026) - add new examples - 32Bit/64Bit Walkthrough is now available in technical Documentation. Includes: - Runtime Binaries and Source Code for .NET Framework:......v2.0, v3.0, v3.5, v4.0 - Tutorials in C# and VB.Net:..............................................................COM Proxy Management, Events, etc. - Examples in C# and VB.Net:............................................................Excel, Word, Outlook, PowerPoint, Access - COMAddi...Reusable Library: V1.1.3: A collection of reusable abstractions for enterprise application developerClosedXML - The easy way to OpenXML: ClosedXML 0.54.0: New on this release: 1) Mayor performance improvements. 2) AdjustToContents now take into account the text rotation. 3) Fixed issues 6782, 6784, 6788HTML-IDEx: HTML-IDEx .15 ALPHA: This release fixes line counting a little bit and adds the masshighlight() sub, which highlights pasted and inserted code.AutoLoL: AutoLoL v2.0.3: - Improved summoner spells are now displayed - Fixed some of the startup errors people got - Double clicking an item selects it - Some usability changes that make using AutoLoL just a little easier - Bug fixes AutoLoL v2 is not an update, but an entirely new version! Please install to a different directory than AutoLoL v1Host Profiles: Host Profiles 1.0: Host Profiles 1.0 Release Quickly modify host file Automatically flush dnsVidCoder: 0.9.2: Updated to HandBrake 4024svn. This fixes problems with mpeg2 sources: corrupted previews, incorrect progress indicators and encodes that incorrectly report as failed. Fixed a problem that prevented target sizes above 2048 MB.SharePoint Search XSL Samples: SharePoint 2010 Samples: I have updated some of the samples from the 2007 release. These all work in SharePoint 2010. I removed the Pivot on File Extension because SharePoint 2010 search has refiners that perform the same function.AcDown????? - Anime&Comic Downloader: AcDown????? v3.0 Beta5: ??AcDown?????????????，??????????????，????、????。?????Acfun????? ????32??64? Windows XP/Vista/7 ????????????? ??：????????Windows XP???,?????????.NET Framework 2.0???(x86)?.NET Framework 2.0???(x64)，?????"?????????"??? ??v3.0 Beta5 ?????????? ???? ?? ???????? ???"????????"?? ????????????? ????????/???? ?? ???"????"??? ?? ??????????? ?? ?? ??????????? ?? ?????????????????? ??????????????????? ???????????????? ????????????Discussions???????? ????AcDown??????????????VFPX: GoFish 4 Beta 1: Current beta is Build 144 (released 2011-06-07 ) See the GoFish4 info page for details and video link: http://vfpx.codeplex.com/wikipage?title=GoFishShowUI: Write-UI -in PowerShell: ShowUI: ShowUI is a PowerShell module to help you write rich user interfaces in script.SharePoint 2010 FBA Pack: SharePoint 2010 FBA Pack 1.0.3: Fixed User Management screen when "RequiresQuestionAndAnswer" set to true Reply to Email Address can now be customized User Management page now only displays users that reside in the membership database Web parts have been changed to inherit from System.Web.UI.WebControls.WebParts.WebPart, so that they will display on anonymous application pages For installation and configuration steps see here.TerrariViewer: TerrariViewer v2.5: Added new items associated with Terraria v1.0.3 to the character editor. Fixed multiple bugs with Piggy Bank EditoryNew Projects.NET MVC Base by OST: The OST .NET MVC project is currently in infancy but contains html helper extensions, model binders and other extensions to the mvc 3 framework. It also contains a separate project for easily consuming JQGrid requests and return the correct JSON to the jQuery plugin.Asterisk AMI Proxy suite: The AMI Proxy suite project will bridge the gap between your asterisk phone system and your windows based applications. The AMI Proxy is a service that can be used to simply proxy AMI connections to your asterisk server but also adds call stat generation and line monitors.Augusta Developers Guild: The web site for the user group Augusta Developers GuildAzure Blob Pusher: File uploader allows bulk upload of files from client to Azure blob storage. FileSystemWatcher notices new files in configured directory. SQL Express database tracks files as they are pushed up to blob storage and then processed. Local Directory is cleaned up after acknowledgement.Basic Class Library: A collection of functions created to eased up the programmers life in order to solved basic task like validation, AmountTowords, Encrypt & Decryption it also has capability to Connect and retrieve sql data just in one line of code, and some other Basic but very Important task.Basic RTS Game using RolePlayingGame Tool kit based XNA: this is a basic RTS Game. i can make it easy by using RolePlayingGame Took Kit based XNA.Batch Scheduler using .Net 4, MEF and Entity framework 4.1 (Magic Unicorn): Simple Batch Architecture written on C#. Uses the .NET 4, MEF and Entity Framework 4.1 Code First. If you dont need a scheduler, just use the sample code. Agents can be scheduled through a central database table. Plug-ins (or jobs) are launched through MEF. DropBox Linker: The goal of DropBox Linker project is to improve DropBox service client usability. It intellectually automates copying URLs to clipboard after publishing a file. Multiple files at once is supported. Additionally, it corrects URL on file rename after its link been copied.Exchange Spigot for NodeXL: Exchange Spigot for NodeXL enables Microsoft Excel plugin NodeXL to collect messaging data from the Microsoft Exchange Server and display that data as a graph. It is developed in C#.G - Low Level Graphics API: A low level graphics api, in similar style to OpenGL, but more OO. Can drastically speed up OpenGL based apps. Makes full use of Net4.0 features such as lambada expressions where useful. (C#, OpenTK powered. This is not for C++) GpgAPI - A C# Api for Gpg: GpgAPI is a C# API for Gpg. Gpg is a command line software to encrypt, decrypt files with a symmetric or assymetric key. You can also managed public keys, import keys from the web, export your public keys, etc. GpgAPI is an interface to Gpg. In C#, with a few lines, you can execute gpg to encrypt, decrypt, etc. The license of this project is "GPL v3"; it is NOT GPL v2. GPL v3 is not present in the licenses list so I had to choose GPL v2. So if use GpgAPI, you must accept the GPL v...iDreamBoard: iDreamBoard is an application to ease the process of creating and editing dreamboard themes for iOS devices. UNDER DEVELOPMENTIETouch: Use IE Touch to access multitouch events from JavaScript in IE. This project uses some of the code from Windows 7 Multitouch .NET Interop Sample Library available in http://archive.msdn.microsoft.com/WindowsTouch/Release/ProjectReleases.aspx?ReleaseId=2127iMaker-Lion: Applications post installation pour Mac OS X sur PC.Informatic System Ma Chung University Alumni Center: Informatic System Ma Chung University Alumni Center is a website for alumni at Information System Faculty at Ma Chung University at Malang, IndonesiaJasc (just another script compressor): Just another script compressor, but that's by far the easiest to use! Use Jasc to merge compress your javascript (JS) and style sheets (CSS). Just drop the executable in your javascript / CSS folder and run it. Voyla! It will handle everything by itself. Compression is based on Microsoft Ajax Minifier. Jasc can handle single or multiple files, will accept regular expressions to remove specific lines from the source code, and can also optimize the results by shrinking variable names and twe...LINQ Extensions Library: A library of useful LINQ extensions allowing for arithmetic manipulation of sequences, statistical analysis, sequence generation, sequence manipulation, pattern detection and more.Mail2FotoFrame: Pulls emails from a POP3-Account, extracts picture-attachments and saves them to a SD-card, so you can view them on a fotoframe.Make web (or sharepoint) pages screenshots with Powershell: From a text file containing url, make screenshot of each page. This powershell script use iecapt.exe project. You can manage width format and delay for each captureModé Internationalé (E-Commerce Site): Mode International is a fictional clothing store, and this website project is meant to be the e-Commerce site for this store. So far, the project has been developed using Java Enterprise Edition and Sockets, but I am considering making the use of C# in ASP .NET in the future.Music House: Site dedicado a musica e afiliadosNiphor's ToolBox: ?????????Nordic nRF24L01+ .NET Micro Framework Driver: Library that enables .NET Micro Framework developers to use Nordic 2.4 GHz wireless tranceivers. This library can be used on any net mf device with SPI interface.Petey's Game Engine: Petey's Game Engine is a XNA 4.0 game engine with a featured blog describing each step of the development. This is a learning project so people may follow and learn as my project evolves.ReportGenerator: ReportGenerator converts XML reports generated by PartCover or NCover into a readable HTML report.Rise of the rabbits: Rise of the RabbitsSapaFinance: SapaFinanceSCSM Copy Object: SCSM Copy Object is a CodePlex project that enables users to select objects in the System Center Service Manager console, click a task in the task pane and create a copy of the selected object(s). Objects can also be copied from command line executables.SharePoint 2010 Language Pack Downloader: SharePoint 2010 Language Pack Downloader is a tool to quickly download multiple language pack files for the SharePoint 2010 Server platform.SharePoint XQuery Reporting Solution: My company's project needs this technology because of the current company has a lot of data is stored in SharePoint, through Infopath data collection, data storage and not all InfoPath field values ​​are saved into a database, a considerable number of data in XML File, which caused difficulties in query and print a report, need a solution. Simply explained the thinking: First step:Put SharePoint, InfoPath XML file later (I did a small tool XMLToDB) or through the Event Handle sync sav...The Pacman: A simple single player game similar to Pacman. Developed using XNA game framework and C#. Game demonstrates usage of fuzzy logic for controlling the AI ghosts. This game is developed to test the effect of fuzzy logic AI in Pacman game.TodoStrike: Todo Strike is a simple todo list keeper.WallpaperDeleter: Simple program to delete the current background wallpaper image.Windows Phone 7 Continuous Integration Testing Framework: WP7 CI is a port of the Silverlight Toolkit Test Framework with added CI support, allowing tests to be run in the emulator from the command lineWolfpack - Distributed System Monitoring: Wolfpack is an extensible, .Net windows service framework for running jobs to monitor your software, system & business KPI's. The data collected can be sent directly to Growl, Geckoboard, WCF, SQL, SQLite, NServiceBus. It comes loaded with some tasks but it's simple to implement your own!

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• How to speed up this simple mysql query?

  - by Jim Thio

  The query is simple: SELECT TB.ID, TB.Latitude, TB.Longitude, 111151.29341326*SQRT(pow(-6.185-TB.Latitude,2)+pow(106.773-TB.Longitude,2)*cos(-6.185*0.017453292519943)*cos(TB.Latitude*0.017453292519943)) AS Distance FROM `tablebusiness` AS TB WHERE -6.2767668133836 < TB.Latitude AND TB.Latitude < -6.0932331866164 AND FoursquarePeopleCount >5 AND 106.68123318662 < TB.Longitude AND TB.Longitude <106.86476681338 ORDER BY Distance See, we just look at all business within a rectangle. 1.6 million rows. Within that small rectangle there are only 67,565 businesses. The structure of the table is 1 ID varchar(250) utf8_unicode_ci No None Change Change Drop Drop More Show more actions 2 Email varchar(400) utf8_unicode_ci Yes NULL Change Change Drop Drop More Show more actions 3 InBuildingAddress varchar(400) utf8_unicode_ci Yes NULL Change Change Drop Drop More Show more actions 4 Price int(10) Yes NULL Change Change Drop Drop More Show more actions 5 Street varchar(400) utf8_unicode_ci Yes NULL Change Change Drop Drop More Show more actions 6 Title varchar(400) utf8_unicode_ci Yes NULL Change Change Drop Drop More Show more actions 7 Website varchar(400) utf8_unicode_ci Yes NULL Change Change Drop Drop More Show more actions 8 Zip varchar(400) utf8_unicode_ci Yes NULL Change Change Drop Drop More Show more actions 9 Rating Star double Yes NULL Change Change Drop Drop More Show more actions 10 Rating Weight double Yes NULL Change Change Drop Drop More Show more actions 11 Latitude double Yes NULL Change Change Drop Drop More Show more actions 12 Longitude double Yes NULL Change Change Drop Drop More Show more actions 13 Building varchar(200) utf8_unicode_ci Yes NULL Change Change Drop Drop More Show more actions 14 City varchar(100) utf8_unicode_ci No None Change Change Drop Drop More Show more actions 15 OpeningHour varchar(400) utf8_unicode_ci Yes NULL Change Change Drop Drop More Show more actions 16 TimeStamp timestamp on update CURRENT_TIMESTAMP No CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP Change Change Drop Drop More Show more actions 17 CountViews int(11) Yes NULL Change Change Drop Drop More Show more actions The indexes are: Edit Edit Drop Drop PRIMARY BTREE Yes No ID 1965990 A Edit Edit Drop Drop City BTREE No No City 131066 A Edit Edit Drop Drop Building BTREE No No Building 21 A YES Edit Edit Drop Drop OpeningHour BTREE No No OpeningHour (255) 21 A YES Edit Edit Drop Drop Email BTREE No No Email (255) 21 A YES Edit Edit Drop Drop InBuildingAddress BTREE No No InBuildingAddress (255) 21 A YES Edit Edit Drop Drop Price BTREE No No Price 21 A YES Edit Edit Drop Drop Street BTREE No No Street (255) 982995 A YES Edit Edit Drop Drop Title BTREE No No Title (255) 1965990 A YES Edit Edit Drop Drop Website BTREE No No Website (255) 491497 A YES Edit Edit Drop Drop Zip BTREE No No Zip (255) 178726 A YES Edit Edit Drop Drop Rating Star BTREE No No Rating Star 21 A YES Edit Edit Drop Drop Rating Weight BTREE No No Rating Weight 21 A YES Edit Edit Drop Drop Latitude BTREE No No Latitude 1965990 A YES Edit Edit Drop Drop Longitude BTREE No No Longitude 1965990 A YES The query took forever. I think there has to be something wrong there. Showing rows 0 - 29 ( 67,565 total, Query took 12.4767 sec)

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• How to implement a simple bullet trajectory

  - by AirieFenix

  I searched and searched and although it's a fair simple question, I don't find the proper answer but general ideas (which I already have). I have a top-down game and I want to implement a gun which shoots bullets that follow a simple path (no physics nor change of trajectory, just go from A to B thing). a: vector of the position of the gun/player. b: vector of the mouse position (cross-hair). w: the vector of the bullet's trajectory. So, w=b-a. And the position of the bullet = [x=x0+speed*time*normalized w.x , y=y0+speed*time * normalized w.y]. I have the constructor: public Shot(int shipX, int shipY, int mouseX, int mouseY) { //I get mouse with Gdx.input.getX()/getY() ... this.shotTime = TimeUtils.millis(); this.posX = shipX; this.posY = shipY; //I used aVector = aVector.nor() here before but for some reason didn't work float tmp = (float) (Math.pow(mouseX-shipX, 2) + Math.pow(mouseY-shipY, 2)); tmp = (float) Math.sqrt(Math.abs(tmp)); this.vecX = (mouseX-shipX)/tmp; this.vecY = (mouseY-shipY)/tmp; } And here I update the position and draw the shot: public void drawShot(SpriteBatch batch) { this.lifeTime = TimeUtils.millis() - this.shotTime; //position = positionBefore + v*t this.posX = this.posX + this.vecX*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); this.posY = this.posY + this.vecY*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); ... } Now, the behavior of the bullet seems very awkward, not going exactly where my mouse is (it's like the mouse is 30px off) and with a random speed. I know I probably need to open the old algebra book from college but I'd like somebody says if I'm in the right direction (or points me to it); if it's a calculation problem, a code problem or both. Also, is it possible that Gdx.input.getX() gives me non-precise position? Because when I draw the cross-hair it also draws off the cursor position. Sorry for the long post and sorry if it's a very basic question. Thanks!

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• determine collision angle on a rotating body

  - by jorb

  update: new diagram and updated description I have a contact listener set up to try and determine the side that a collision happened at relative to the a bodies rotation. One way to solve this is to find the value of the yellow angle between the red and blue vectors drawn above. The angle can be found by taking the arc cosine of the dot product of the two vectors (Evan pointed this out). One of my points of confusion is the difference in domain of the atan2 function html canvas coordinates and the Box2d rotation information. I know I have to account for this somehow... SS below questions: Does Box2D provide these angles more directly in the collision information? Am I even on the right track? If so, any hints? I have the following javascript so far: Ship.prototype.onCollide = function (other_ent,cx,cy) { var pos = this.body.GetPosition(); //collision position relative to body var d_cx = pos.x - cx; var d_cy = pos.y - cy; //length of initial vector var len = Math.sqrt(Math.pow(pos.x -cx,2) + Math.pow(pos.y-cy,2)); //body angle - can over rotate hence mod 2*Pi var ang = this.body.GetAngle() % (Math.PI * 2); //vector representing body's angle - same magnitude as the first var b_vx = len * Math.cos(ang); var b_vy = len * Math.sin(ang); //dot product of the two vectors var dot_prod = d_cx * b_vx + d_cy * b_vy; //new calculation of difference in angle - NOT WORKING! var d_ang = Math.acos(dot_prod); var side; if (Math.abs(d_ang) < Math.PI/2 ) side = "front"; else side = "back"; console.log("length",len); console.log("pos:",pos.x,pos.y); console.log("offs:",d_cx,d_cy); console.log("body vec",b_vx,b_vy); console.log("body angle:",ang); console.log("dot product",dot_prod); console.log("result:",d_ang); console.log("side",side); console.log("------------------------"); }

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• Best way to implement a simple bullet trajectory

  - by AirieFenix

  I searched and searched and although it's a fair simple question, I don't find the proper answer but general ideas (which I already have). I have a top-down game and I want to implement a gun which shoots bullets that follow a simple path (no physics nor change of trajectory, just go from A to B thing). a: vector of the position of the gun/player. b: vector of the mouse position (cross-hair). w: the vector of the bullet's trajectory. So, w=b-a. And the position of the bullet = [x=x0+speed*time*normalized w.x , y=y0+speed*time * normalized w.y]. I have the constructor: public Shot(int shipX, int shipY, int mouseX, int mouseY) { //I get mouse with Gdx.input.getX()/getY() ... this.shotTime = TimeUtils.millis(); this.posX = shipX; this.posY = shipY; //I used aVector = aVector.nor() here before but for some reason didn't work float tmp = (float) (Math.pow(mouseX-shipX, 2) + Math.pow(mouseY-shipY, 2)); tmp = (float) Math.sqrt(Math.abs(tmp)); this.vecX = (mouseX-shipX)/tmp; this.vecY = (mouseY-shipY)/tmp; } And here I update the position and draw the shot: public void drawShot(SpriteBatch batch) { this.lifeTime = TimeUtils.millis() - this.shotTime; //position = positionBefore + v*t this.posX = this.posX + this.vecX*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); this.posY = this.posY + this.vecY*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); ... } Now, the behavior of the bullet seems very awkward, not going exactly where my mouse is (it's like the mouse is 30px off) and with a random speed. I know I probably need to open the old algebra book from college but I'd like somebody says if I'm in the right direction (or points me to it); if it's a calculation problem, a code problem or both. Also, is it possible that Gdx.input.getX() gives me non-precise position? Because when I draw the cross-hair it also draws off the cursor position. Sorry for the long post and sorry if it's a very basic question. Thanks!

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• Bump mapping Problem GLSL

  - by jmfel1926

  I am having a slight problem with my Bump Mapping project. Although everything works OK (at least from what I know) there is a slight mistake somewhere and I get incorrect shading on the brick wall when the light goes to the one side or the other as seen in the picture below: The light is on the right side so the shading on the wall should be the other way. I have provided the shaders to help find the issue (I do not have much experience with shaders). Shaders: varying vec3 viewVec; varying vec3 position; varying vec3 lightvec; attribute vec3 tangent; attribute vec3 binormal; uniform vec3 lightpos; uniform mat4 cameraMat; void main() { gl_TexCoord[0] = gl_MultiTexCoord0; gl_Position = ftransform(); position = vec3(gl_ModelViewMatrix * gl_Vertex); lightvec = vec3(cameraMat * vec4(lightpos,1.0)) - position ; vec3 eyeVec = vec3(gl_ModelViewMatrix * gl_Vertex); viewVec = normalize(-eyeVec); } uniform sampler2D colormap; uniform sampler2D normalmap; varying vec3 viewVec; varying vec3 position; varying vec3 lightvec; vec3 vv; uniform float diffuset; uniform float specularterm; uniform float ambientterm; void main() { vv=viewVec; vec3 normals = normalize(texture2D(normalmap,gl_TexCoord[0].st).rgb * 2.0 - 1.0); normals.y = -normals.y; //normals = (normals * gl_NormalMatrix).xyz ; vec3 distance = lightvec; float dist_number =length(distance); float final_dist_number = 2.0/pow(dist_number,diffuset); vec3 light_dir=normalize(lightvec); vec3 Halfvector = normalize(light_dir+vv); float angle=max(dot(Halfvector,normals),0.0); angle= pow(angle,specularterm); vec3 specular=vec3(angle,angle,angle); float diffuseterm=max(dot(light_dir,normals),0.0); vec3 diffuse = diffuseterm * texture2D(colormap,gl_TexCoord[0].st).rgb; vec3 ambient = ambientterm *texture2D(colormap,gl_TexCoord[0].st).rgb; vec3 diffusefinal = diffuse * final_dist_number; vec3 finalcolor=diffusefinal+specular+ambient; gl_FragColor = vec4(finalcolor, 1.0); }

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• Atmospheric scattering OpenGL 3.3

  - by user1419305

  Im currently trying to convert a shader by Sean O'Neil to version 330 so i can try it out in a application im writing. Im having some issues with deprecated functions, so i replaced them, but im almost completely new to glsl, so i probably did a mistake somewhere. Original shaders can be found here: http://www.gamedev.net/topic/592043-solved-trying-to-use-atmospheric-scattering-oneill-2004-but-get-black-sphere/ My horrible attempt at converting them: Vertex Shader: #version 330 core layout(location = 0) in vec3 vertexPosition_modelspace; //layout(location = 1) in vec2 vertexUV; layout(location = 2) in vec3 vertexNormal_modelspace; uniform vec3 v3CameraPos; uniform vec3 v3LightPos; uniform vec3 v3InvWavelength; uniform float fCameraHeight; uniform float fCameraHeight2; uniform float fOuterRadius; uniform float fOuterRadius2; uniform float fInnerRadius; uniform float fInnerRadius2; uniform float fKrESun; uniform float fKmESun; uniform float fKr4PI; uniform float fKm4PI; uniform float fScale; uniform float fScaleDepth; uniform float fScaleOverScaleDepth; // passing in matrixes for transformations uniform mat4 MVP; uniform mat4 V; uniform mat4 M; const int nSamples = 4; const float fSamples = 4.0; out vec3 v3Direction; out vec4 gg_FrontColor; out vec4 gg_FrontSecondaryColor; float scale(float fCos) { float x = 1.0 - fCos; return fScaleDepth * exp(-0.00287 + x*(0.459 + x*(3.83 + x*(-6.80 + x*5.25)))); } void main(void) { vec3 v3Pos = vertexPosition_modelspace; vec3 v3Ray = v3Pos - v3CameraPos; float fFar = length(v3Ray); v3Ray /= fFar; vec3 v3Start = v3CameraPos; float fHeight = length(v3Start); float fDepth = exp(fScaleOverScaleDepth * (fInnerRadius - fCameraHeight)); float fStartAngle = dot(v3Ray, v3Start) / fHeight; float fStartOffset = fDepth*scale(fStartAngle); float fSampleLength = fFar / fSamples; float fScaledLength = fSampleLength * fScale; vec3 v3SampleRay = v3Ray * fSampleLength; vec3 v3SamplePoint = v3Start + v3SampleRay * 0.5; vec3 v3FrontColor = vec3(0.0, 0.0, 0.0); for(int i=0; i<nSamples; i++) { float fHeight = length(v3SamplePoint); float fDepth = exp(fScaleOverScaleDepth * (fInnerRadius - fHeight)); float fLightAngle = dot(v3LightPos, v3SamplePoint) / fHeight; float fCameraAngle = dot(v3Ray, v3SamplePoint) / fHeight; float fScatter = (fStartOffset + fDepth*(scale(fLightAngle) - scale(fCameraAngle))); vec3 v3Attenuate = exp(-fScatter * (v3InvWavelength * fKr4PI + fKm4PI)); v3FrontColor += v3Attenuate * (fDepth * fScaledLength); v3SamplePoint += v3SampleRay; } gg_FrontSecondaryColor.rgb = v3FrontColor * fKmESun; gg_FrontColor.rgb = v3FrontColor * (v3InvWavelength * fKrESun); gl_Position = MVP * vec4(vertexPosition_modelspace,1); v3Direction = v3CameraPos - v3Pos; } Fragment Shader: #version 330 core uniform vec3 v3LightPos; uniform float g; uniform float g2; in vec3 v3Direction; out vec4 FragColor; in vec4 gg_FrontColor; in vec4 gg_FrontSecondaryColor; void main (void) { float fCos = dot(v3LightPos, v3Direction) / length(v3Direction); float fMiePhase = 1.5 * ((1.0 - g2) / (2.0 + g2)) * (1.0 + fCos*fCos) / pow(1.0 + g2 - 2.0*g*fCos, 1.5); FragColor = gg_FrontColor + fMiePhase * gg_FrontSecondaryColor; FragColor.a = FragColor.b; } I wrote a function to render a sphere, and im trying to render this shader onto a inverted version of it, the sphere works completely fine, with normals and all. My problem is that the sphere gets rendered all black, so the shader is not working. This is how i'm trying to render the atmosphere inside my main rendering loop. glUseProgram(programAtmosphere); glBindTexture(GL_TEXTURE_2D, 0); //###################### glUniform3f(v3CameraPos, getPlayerPos().x, getPlayerPos().y, getPlayerPos().z); glUniform3f(v3LightPos, lightPos.x / sqrt(lightPos.x * lightPos.x + lightPos.y * lightPos.y), lightPos.y / sqrt(lightPos.x * lightPos.x + lightPos.y * lightPos.y), 0); glUniform3f(v3InvWavelength, 1.0 / pow(0.650, 4.0), 1.0 / pow(0.570, 4.0), 1.0 / pow(0.475, 4.0)); glUniform1fARB(fCameraHeight, 1); glUniform1fARB(fCameraHeight2, 1); glUniform1fARB(fInnerRadius, 6350); glUniform1fARB(fInnerRadius2, 6350 * 6350); glUniform1fARB(fOuterRadius, 6450); glUniform1fARB(fOuterRadius2, 6450 * 6450); glUniform1fARB(fKrESun, 0.0025 * 20.0); glUniform1fARB(fKmESun, 0.0015 * 20.0); glUniform1fARB(fKr4PI, 0.0025 * 4.0 * 3.141592653); glUniform1fARB(fKm4PI, 0.0015 * 4.0 * 3.141592653); glUniform1fARB(fScale, 1.0 / (6450 - 6350)); glUniform1fARB(fScaleDepth, 0.25); glUniform1fARB(fScaleOverScaleDepth, 4.0 / (6450 - 6350)); glUniform1fARB(g, -0.85); glUniform1f(g2, -0.85 * -0.85); // vertices glEnableVertexAttribArray(0); glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer[1]); glVertexAttribPointer( 0, // attribute 3, // size GL_FLOAT, // type GL_FALSE, // normalized? 0, // stride (void*)0 // array buffer offset ); // normals glEnableVertexAttribArray(2); glBindBuffer(GL_ARRAY_BUFFER, normalbuffer[1]); glVertexAttribPointer( 2, // attribute 3, // size GL_FLOAT, // type GL_FALSE, // normalized? 0, // stride (void*)0 // array buffer offset ); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementbuffer[1]); glUniformMatrix4fv(ModelMatrixAT, 1, GL_FALSE, &ModelMatrix[0][0]); glUniformMatrix4fv(ViewMatrixAT, 1, GL_FALSE, &ViewMatrix[0][0]); glUniformMatrix4fv(ModelViewPAT, 1, GL_FALSE, &MVP[0][0]); // Draw the triangles glDrawElements( GL_TRIANGLES, // mode cubeIndices[1], // count GL_UNSIGNED_SHORT, // type (void*)0 // element array buffer offset ); Any ideas?

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• Java code optimization leads to numerical inaccuracies and errors

  - by rano

  I'm trying to implement a version of the Fuzzy C-Means algorithm in Java and I'm trying to do some optimization by computing just once everything that can be computed just once. This is an iterative algorithm and regarding the updating of a matrix, the clusters x pixels membership matrix U, this is the update rule I want to optimize: where the x are the element of a matrix X (pixels x features) and v belongs to the matrix V (clusters x features). And m is a parameter that ranges from 1.1 to infinity. The distance used is the euclidean norm. If I had to implement this formula in a banal way I'd do: for(int i = 0; i < X.length; i++) { int count = 0; for(int j = 0; j < V.length; j++) { double num = D[i][j]; double sumTerms = 0; for(int k = 0; k < V.length; k++) { double thisDistance = D[i][k]; sumTerms += Math.pow(num / thisDistance, (1.0 / (m - 1.0))); } U[i][j] = (float) (1f / sumTerms); } } In this way some optimization is already done, I precomputed all the possible squared distances between X and V and stored them in a matrix D but that is not enough, since I'm cycling througn the elements of V two times resulting in two nested loops. Looking at the formula the numerator of the fraction is independent of the sum so I can compute numerator and denominator independently and the denominator can be computed just once for each pixel. So I came to a solution like this: int nClusters = V.length; double exp = (1.0 / (m - 1.0)); for(int i = 0; i < X.length; i++) { int count = 0; for(int j = 0; j < nClusters; j++) { double distance = D[i][j]; double denominator = D[i][nClusters]; double numerator = Math.pow(distance, exp); U[i][j] = (float) (1f / (numerator * denominator)); } } Where I precomputed the denominator into an additional column of the matrix D while I was computing the distances: for (int i = 0; i < X.length; i++) { for (int j = 0; j < V.length; j++) { double sum = 0; for (int k = 0; k < nDims; k++) { final double d = X[i][k] - V[j][k]; sum += d * d; } D[i][j] = sum; D[i][B.length] += Math.pow(1 / D[i][j], exp); } } By doing so I encounter numerical differences between the 'banal' computation and the second one that leads to different numerical value in U (not in the first iterates but soon enough). I guess that the problem is that exponentiate very small numbers to high values (the elements of U can range from 0.0 to 1.0 and exp , for m = 1.1, is 10) leads to ver y small values, whereas by dividing the numerator and the denominator and THEN exponentiating the result seems to be better numerically. The problem is it involves much more operations. Am I doing something wrong? Is there a possible solution to get both the code optimized and numerically stable? Any suggestion or criticism will be appreciated.

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• Can't get Jacobi algorithm to work in Objective-C

  - by Chris Long

  Hi, For some reason, I can't get this program to work. I've had other CS majors look at it and they can't figure it out either. This program performs the Jacobi algorithm (you can see step-by-step instructions and a MATLAB implementation here). BTW, it's different from the Wikipedia article of the same name. Since NSArray is one-dimensional, I added a method that makes it act like a two-dimensional C array. After running the Jacobi algorithm many times, the diagonal entries in the NSArray (i[0][0], i[1][1], etc.) are supposed to get bigger and the others approach 0. For some reason though, they all increase exponentially. For instance, i[2][4] should equal 0.0000009, not 9999999, while i[2][2] should be big. Thanks in advance, Chris NSArray+Matrix.m @implementation NSArray (Matrix) @dynamic offValue, transposed; - (double)offValue { double sum = 0.0; for ( MatrixItem *item in self ) if ( item.nonDiagonal ) sum += pow( item.value, 2.0 ); return sum; } - (NSMutableArray *)transposed { NSMutableArray *transpose = [[[NSMutableArray alloc] init] autorelease]; int i, j; for ( i = 0; i < 5; i++ ) { for ( j = 0; j < 5; j++ ) { [transpose addObject:[self objectAtRow:j andColumn:i]]; } } return transpose; } - (id)objectAtRow:(NSUInteger)row andColumn:(NSUInteger)column { NSUInteger index = 5 * row + column; return [self objectAtIndex:index]; } - (NSMutableArray *)multiplyWithMatrix:(NSArray *)array { NSMutableArray *result = [[NSMutableArray alloc] init]; int i = 0, j = 0, k = 0; double value; for ( i = 0; i < 5; i++ ) { value = 0.0; for ( j = 0; j < 5; j++ ) { for ( k = 0; k < 5; k++ ) { MatrixItem *firstItem = [self objectAtRow:i andColumn:k]; MatrixItem *secondItem = [array objectAtRow:k andColumn:j]; value += firstItem.value * secondItem.value; } MatrixItem *item = [[MatrixItem alloc] initWithValue:value]; item.row = i; item.column = j; [result addObject:item]; } } return result; } @end Jacobi_AlgorithmAppDelegate.m // ... - (void)jacobiAlgorithmWithEntry:(MatrixItem *)entry { MatrixItem *b11 = [matrix objectAtRow:entry.row andColumn:entry.row]; MatrixItem *b22 = [matrix objectAtRow:entry.column andColumn:entry.column]; double muPlus = ( b22.value + b11.value ) / 2.0; muPlus += sqrt( pow((b22.value - b11.value), 2.0) + 4.0 * pow(entry.value, 2.0) ); Vector *u1 = [[[Vector alloc] initWithX:(-1.0 * entry.value) andY:(b11.value - muPlus)] autorelease]; [u1 normalize]; Vector *u2 = [[[Vector alloc] initWithX:-u1.y andY:u1.x] autorelease]; NSMutableArray *g = [[[NSMutableArray alloc] init] autorelease]; for ( int i = 0; i <= 24; i++ ) { MatrixItem *item = [[[MatrixItem alloc] init] autorelease]; if ( i == 6*entry.row ) item.value = u1.x; else if ( i == 6*entry.column ) item.value = u2.y; else if ( i == ( 5*entry.row + entry.column ) || i == ( 5*entry.column + entry.row ) ) item.value = u1.y; else if ( i % 6 == 0 ) item.value = 1.0; else item.value = 0.0; [g addObject:item]; } NSMutableArray *firstResult = [[g.transposed multiplyWithMatrix:matrix] autorelease]; matrix = [firstResult multiplyWithMatrix:g]; } // ...

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• Incorrect lighting results with deferred rendering

  - by Lasse

  I am trying to render a light-pass to a texture which I will later apply on the scene. But I seem to calculate the light position wrong. I am working on view-space. In the image above, I am outputting the attenuation of a point light which is currently covering the whole screen. The light is at 0,10,0 position, and I transform it to view-space first: Vector4 pos; Vector4 tmp = new Vector4 (light.Position, 1); // Transform light position for shader Vector4.Transform (ref tmp, ref Camera.ViewMatrix, out pos); shader.SendUniform ("LightViewPosition", ref pos); Now to me that does not look as it should. What I think it should look like is that the white area should be on the center of the scene. The camera is at the corner of the scene, and it seems as if the light would move along with the camera. Here's the fragment shader code: void main(){ // default black color vec3 color = vec3(0); // Pixel coordinates on screen without depth vec2 PixelCoordinates = gl_FragCoord.xy / ScreenSize; // Get pixel position using depth from texture vec4 depthtexel = texture( DepthTexture, PixelCoordinates ); float depthSample = unpack_depth(depthtexel); // Get pixel coordinates on camera-space by multiplying the // coordinate on screen-space by inverse projection matrix vec4 world = (ImP * RemapMatrix * vec4(PixelCoordinates, depthSample, 1.0)); // Undo the perspective calculations vec3 pixelPosition = (world.xyz / world.w) * 3; // How far the light should reach from it's point of origin float lightReach = LightColor.a / 2; // Vector in between light and pixel vec3 lightDir = (LightViewPosition.xyz - pixelPosition); float lightDistance = length(lightDir); vec3 lightDirN = normalize(lightDir); // Discard pixels too far from light source //if(lightReach < lightDistance) discard; // Get normal from texture vec3 normal = normalize((texture( NormalTexture, PixelCoordinates ).xyz * 2) - 1); // Half vector between the light direction and eye, used for specular component vec3 halfVector = normalize(lightDirN + normalize(-pixelPosition)); // Dot product of normal and light direction float NdotL = dot(normal, lightDirN); float attenuation = pow(lightReach / lightDistance, LightFalloff); // If pixel is lit by the light if(NdotL > 0) { // I have moved stuff from here to above so I can debug them. // Diffuse light color color += LightColor.rgb * NdotL * attenuation; // Specular light color color += LightColor.xyz * pow(max(dot(halfVector, normal), 0.0), 4.0) * attenuation; } RT0 = vec4(color, 1); //RT0 = vec4(pixelPosition, 1); //RT0 = vec4(depthSample, depthSample, depthSample, 1); //RT0 = vec4(NdotL, NdotL, NdotL, 1); RT0 = vec4(attenuation, attenuation, attenuation, 1); //RT0 = vec4(lightReach, lightReach, lightReach, 1); //RT0 = depthtexel; //RT0 = 100 / vec4(lightDistance, lightDistance, lightDistance, 1); //RT0 = vec4(lightDirN, 1); //RT0 = vec4(halfVector, 1); //RT0 = vec4(LightColor.xyz,1); //RT0 = vec4(LightViewPosition.xyz/100, 1); //RT0 = vec4(LightPosition.xyz, 1); //RT0 = vec4(normal,1); } What am I doing wrong here?

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• Prevent full table scan for query with multiple where clauses

  - by Dave Jarvis

  A while ago I posted a message about optimizing a query in MySQL. I have since ported the data and query to PostgreSQL, but now PostgreSQL has the same problem. The solution in MySQL was to force the optimizer to not optimize using STRAIGHT_JOIN. PostgreSQL offers no such option. Here is the explain: Here is the query: SELECT avg(d.amount) AS amount, y.year FROM station s, station_district sd, year_ref y, month_ref m, daily d LEFT JOIN city c ON c.id = 10663 WHERE -- Find all the stations within a specific unit radius ... -- 6371.009 * SQRT( POW(RADIANS(c.latitude_decimal - s.latitude_decimal), 2) + (COS(RADIANS(c.latitude_decimal + s.latitude_decimal) / 2) * POW(RADIANS(c.longitude_decimal - s.longitude_decimal), 2)) ) <= 50 AND -- Ignore stations outside the given elevations -- s.elevation BETWEEN 0 AND 2000 AND sd.id = s.station_district_id AND -- Gather all known years for that station ... -- y.station_district_id = sd.id AND -- The data before 1900 is shaky; insufficient after 2009. -- y.year BETWEEN 1980 AND 2000 AND -- Filtered by all known months ... -- m.year_ref_id = y.id AND m.month = 12 AND -- Whittled down by category ... -- m.category_id = '001' AND -- Into the valid daily climate data. -- m.id = d.month_ref_id AND d.daily_flag_id <> 'M' GROUP BY y.year It appears as though PostgreSQL is looking at the DAILY table first, which is simply not the right way to go about this query as there are nearly 300 million rows. How do I force PostgreSQL to start at the CITY table? Thank you!

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• Why does division yield a vastly different result than multiplication by a fraction in floating points.

  - by Avram

  I understand why floating point numbers can't be compared, and know about the mantissa and exponent binary representation, but I'm no expert and today I came across something I don't get: Namely lets say you have something like: float denominator, numerator, resultone, resulttwo; resultone = numerator / denominator; float buff = 1 / denominator; resulttwo = numerator * buff; To my knowledge different flops can yield different results and this is not unusual. But in some edge cases these two results seem to be vastly different. To be more specific in my GLSL code calculating the Beckmann facet slope distribution for the Cook-Torrance lighitng model: float a = 1 / (facetSlopeRMS * facetSlopeRMS * pow(clampedCosHalfNormal, 4)); float b = clampedCosHalfNormal * clampedCosHalfNormal - 1.0; float c = facetSlopeRMS * facetSlopeRMS * clampedCosHalfNormal * clampedCosHalfNormal; facetSlopeDistribution = a * exp(b/c); yields very very different results to float a = (facetSlopeRMS * facetSlopeRMS * pow(clampedCosHalfNormal, 4)); facetDlopeDistribution = exp(b/c) / a; Why does it? The second form of the expression is problematic. If I say try to add the second form of the expression to a color I get blacks, even though the expression should always evaluate to a positive number. Am I getting an infinity? A NaN? if so why?

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• Beginner problems with references to arrays in python 3.1.1

  - by Protean

  As part of the last assignment in a beginner python programing class, I have been assigned a traveling sales man problem. I settled on a recursive function to find each permutation and the sum of the distances between the destinations, however, I am have a lot of problems with references. Arrays in different instances of the Permute and Main functions of TSP seem to be pointing to the same reference. from math import sqrt class TSP: def __init__(self): self.CartisianCoordinates = [['A',[1,1]], ['B',[2,2]], ['C',[2,1]], ['D',[1,2]], ['E',[3,3]]] self.Array = [] self.Max = 0 self.StoredList = ['',0] def Distance(self, i1, i2): x1 = self.CartisianCoordinates[i1][1][0] y1 = self.CartisianCoordinates[i1][1][1] x2 = self.CartisianCoordinates[i2][1][0] y2 = self.CartisianCoordinates[i2][1][1] return sqrt(pow((x2 - x1), 2) + pow((y2 - y1), 2)) def Evaluate(self): temparray = [] Data = [] for i in range(len(self.CartisianCoordinates)): Data.append([]) for i1 in range(len(self.CartisianCoordinates)): for i2 in range(len(self.CartisianCoordinates)): if i1 != i2: temparray.append(self.Distance(i1, i2)) else: temparray.append('X') Data[i1] = temparray temparray = [] self.Array = Data self.Max = len(Data) def Permute(self,varray,index,vcarry,mcarry): #Problem Class array = varray[:] carry = vcarry[:] for i in range(self.Max): print ('ARRAY:', array) print (index,i,carry,array[index][i]) if array[index][i] != 'X': carry[0] += self.CartisianCoordinates[i][0] carry[1] += array[index][i] if len(carry) != self.Max: temparray = array[:] for j in range(self.Max):temparray[j][i] = 'X' index = i mcarry += self.Permute(temparray,index,carry,mcarry) else: return mcarry print ('pass',mcarry) return mcarry def Main(self): out = [] self.Evaluate() for i in range(self.Max): array = self.Array[:] #array appears to maintain the same reference after each copy, resulting in an incorrect array being passed to Permute after the first iteration. print (self.Array[:]) for j in range(self.Max):array[j][i] = 'X' print('I:', i, array) out.append(self.Permute(array,i,[str(self.CartisianCoordinates[i][0]),0],[])) return out SalesPerson = TSP() print(SalesPerson.Main()) It would be greatly appreciated if you could provide me with help in solving the reference problems I am having. Thank you.

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• Calculating odds distribution with 6-sided dice

  - by Stephen

  I'm trying to calculate the odds distribution of a changing number of 6-sided die rolls. For example, 3d6 ranges from 3 to 18 as follows: 3:1, 4:3, 5:6, 6:10, 7:15, 8:21, 9:25, 10:27, 11:27, 12:25, 13:21, 14:15, 15:10, 16:6, 17:3, 18:1 I wrote this php program to calculate it: function distributionCalc($numberDice,$sides=6) { for ( $i=0; $i<pow($sides,$numberDice); $i++) { $sum=0; for ($j=0; $j<$numberDice; $j++) { $sum+=(1+(floor($i/pow($sides,$j))) % $sides); } $distribution[$sum]++; } return $distribution; } The inner $j for-loop uses the magic of the floor and modulus functions to create a base-6 counting sequence with the number of digits being the number of dice, so 3d6 would count as: 111,112,113,114,115,116,121,122,123,124,125,126,131,etc. The function takes the sum of each, so it would read as: 3,4,5,6,7,8,4,5,6,7,8,9,5,etc. It plows through all 3^6 possible results and adds 1 to the corresponding slot in the $distribution array between 3 and 18. Pretty straightforward. However, it only works until about 8d6, afterward i get server time-outs because it's now doing billions of calculations. But I don't think it's necessary because die probability follows a sweet bell-curve distribution. I'm wondering if there's a way to skip the number crunching and go straight to the curve itself. Is there a way to do this, so, for example, with 80d6 (80-480)? Can the distribution be projected without doing 6^80 calculations? I'm not a professional coder and probability is still new to me, so thanks for all the help! Stephen

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• Draw LINE_STRIP with Unity

  - by Boozzz

  For a new project I am thinking about whether to use OpenGL or Unity3d. I have a bit of experience with OpenGL, but I am completely new to Unity. I already read through the Unity documentation and tutorials on the Unity Website. However, I could not find a way to draw a simple Line-Strip with Unity. In the following example (C#, OpenGL/SharpGL) I draw a round trajectory from a predifined point to an obstacle, which can be imagined as a divided circle with midpoint [cx,cy] and radius r. The position (x-y coordinates) of the obstacle is given by obst_x and obst_y. Question 1: How could I do the same with Unity? Question 2: In my new project, I will have to draw quite a lot of such geometric primitives. Does it make any sense to use Unity for those things? void drawCircle(float cx, float cy, float r, const float obst_x, const float obst_y) { float theta = 0.0f, pos_x, pos_y, dist; const float delta = 0.1; glBegin(GL_LINE_STRIP); while (theta < 180) { theta += delta; //get the current angle float x = r * cosf(theta); //calculate the x component float y = r * sinf(theta); //calculate the y component pos_x = x + cx; //calculate current x position pos_y = y + cy; //calculate current y position //calculate distance from current vertex to obstacle dist = sqrt(pow(pos_x - obst_x) + pow(pos_y - obst_y)); //check if current vertex intersects with obstacle if dist <= 0 { break; //stop drawing circle } else { glVertex2f(pos_x, pos_y); //draw vertex } } glEnd(); }

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• Optimal two variable linear regression SQL statement (censoring outliers)

  - by Dave Jarvis

  Problem Am looking to apply the y = mx + b equation (where m is SLOPE, b is INTERCEPT) to a data set, which is retrieved as shown in the SQL code. The values from the (MySQL) query are: SLOPE = 0.0276653965651912 INTERCEPT = -57.2338357550468 SQL Code SELECT ((sum(t.YEAR) * sum(t.AMOUNT)) - (count(1) * sum(t.YEAR * t.AMOUNT))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as SLOPE, ((sum( t.YEAR ) * sum( t.YEAR * t.AMOUNT )) - (sum( t.AMOUNT ) * sum(power(t.YEAR, 2)))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as INTERCEPT FROM (SELECT D.AMOUNT, Y.YEAR FROM CITY C, STATION S, YEAR_REF Y, MONTH_REF M, DAILY D WHERE -- For a specific city ... -- C.ID = 8590 AND -- Find all the stations within a 15 unit radius ... -- SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) <15 AND -- Gather all known years for that station ... -- S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND -- The data before 1900 is shaky; insufficient after 2009. -- Y.YEAR BETWEEN 1900 AND 2009 AND -- Filtered by all known months ... -- M.YEAR_REF_ID = Y.ID AND -- Whittled down by category ... -- M.CATEGORY_ID = '001' AND -- Into the valid daily climate data. -- M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' GROUP BY Y.YEAR ORDER BY Y.YEAR ) t Data The data is visualized here (with five outliers highlighted): Questions How do I return the y value against all rows without repeating the same query to collect and collate the data? That is, how do I "reuse" the list of t values? How would you change the query to eliminate outliers (at an 85% confidence interval)? The following results (to calculate the start and end points of the line) appear incorrect. Why are the results off by ~10 degrees (e.g., outliers skewing the data)? (1900 * 0.0276653965651912) + (-57.2338357550468) = -4.66958228 (2009 * 0.0276653965651912) + (-57.2338357550468) = -1.65405406 I would have expected the 1900 result to be around 10 (not -4.67) and the 2009 result to be around 11.50 (not -1.65). Thank you!

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• Precision of cos(atan2(y,x)) versus using complex <double>, C++

  - by Ivan

  Hi all, I'm writing some coordinate transformations (more specifically the Joukoswky Transform, Wikipedia Joukowsky Transform), and I'm interested in performance, but of course precision. I'm trying to do the coordinate transformations in two ways: 1) Calculating the real and complex parts in separate, using double precision, as below: double r2 = chi.x*chi.x + chi.y*chi.y; //double sq = pow(r2,-0.5*n) + pow(r2,0.5*n); //slow!!! double sq = sqrt(r2); //way faster! double co = cos(atan2(chi.y,chi.x)); double si = sin(atan2(chi.y,chi.x)); Z.x = 0.5*(co*sq + co/sq); Z.y = 0.5*si*sq; where chi and Z are simple structures with double x and y as members. 2) Using complex : Z = 0.5 * (chi + (1.0 / chi)); Where Z and chi are complex . There interesting part is that indeed the case 1) is faster (about 20%), but the precision is bad, giving error in the third decimal number after the comma after the inverse transform, while the complex gives back the exact number. So, the problem is on the cos(atan2), sin(atan2)? But if it is, how the complex handles that? Thanks!

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• Optimal two variable linear regression SQL statement

  - by Dave Jarvis

  Problem Am looking to apply the y = mx + b equation (where m is SLOPE, b is INTERCEPT) to a data set, which is retrieved as shown in the SQL code. The values from the (MySQL) query are: SLOPE = 0.0276653965651912 INTERCEPT = -57.2338357550468 SQL Code SELECT ((sum(t.YEAR) * sum(t.AMOUNT)) - (count(1) * sum(t.YEAR * t.AMOUNT))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as SLOPE, ((sum( t.YEAR ) * sum( t.YEAR * t.AMOUNT )) - (sum( t.AMOUNT ) * sum(power(t.YEAR, 2)))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as INTERCEPT FROM (SELECT D.AMOUNT, Y.YEAR FROM CITY C, STATION S, YEAR_REF Y, MONTH_REF M, DAILY D WHERE -- For a specific city ... -- C.ID = 8590 AND -- Find all the stations within a 5 unit radius ... -- SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) <15 AND -- Gather all known years for that station ... -- S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND -- The data before 1900 is shaky; and insufficient after 2009. -- Y.YEAR BETWEEN 1900 AND 2009 AND -- Filtered by all known months ... -- M.YEAR_REF_ID = Y.ID AND -- Whittled down by category ... -- M.CATEGORY_ID = '001' AND -- Into the valid daily climate data. -- M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' GROUP BY Y.YEAR ORDER BY Y.YEAR ) t Data The data is visualized here: Questions How do I return the y value against all rows without repeating the same query to collect and collate the data? That is, how do I "reuse" the list of t values? How would you change the query to eliminate outliers (at an 85% confidence interval)? The following results (to calculate the start and end points of the line) appear incorrect. Why are the results off by ~10 degrees (e.g., outliers skewing the data)? (1900 * 0.0276653965651912) + (-57.2338357550468) = -4.66958228 (2009 * 0.0276653965651912) + (-57.2338357550468) = -1.65405406 I would have expected the 1900 result to be around 10 (not -4.67) and the 2009 result to be around 11.50 (not -1.65). Thank you!

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• Optimal two variable linear regression calculation

  - by Dave Jarvis

  Problem Am looking to apply the y = mx + b equation (where m is SLOPE, b is INTERCEPT) to a data set, which is retrieved as shown in the SQL code. The values from the (MySQL) query are: SLOPE = 0.0276653965651912 INTERCEPT = -57.2338357550468 SQL Code SELECT ((sum(t.YEAR) * sum(t.AMOUNT)) - (count(1) * sum(t.YEAR * t.AMOUNT))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as SLOPE, ((sum( t.YEAR ) * sum( t.YEAR * t.AMOUNT )) - (sum( t.AMOUNT ) * sum(power(t.YEAR, 2)))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as INTERCEPT, FROM (SELECT D.AMOUNT, Y.YEAR FROM CITY C, STATION S, YEAR_REF Y, MONTH_REF M, DAILY D WHERE -- For a specific city ... -- C.ID = 8590 AND -- Find all the stations within a 15 unit radius ... -- SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) < 15 AND -- Gather all known years for that station ... -- S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND -- The data before 1900 is shaky; insufficient after 2009. -- Y.YEAR BETWEEN 1900 AND 2009 AND -- Filtered by all known months ... -- M.YEAR_REF_ID = Y.ID AND -- Whittled down by category ... -- M.CATEGORY_ID = '001' AND -- Into the valid daily climate data. -- M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' GROUP BY Y.YEAR ORDER BY Y.YEAR ) t Data The data is visualized here: Question The following results (to calculate the start and end points of the line) appear incorrect. Why are the results off by ~10 degrees (e.g., outliers skewing the data)? (1900 * 0.0276653965651912) + (-57.2338357550468) = -4.66958228 (2009 * 0.0276653965651912) + (-57.2338357550468) = -1.65405406 I would have expected the 1900 result to be around 10 (not -4.67) and the 2009 result to be around 11.50 (not -1.65). Related Sites Least absolute deviations Robust regression Thank you!

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