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• Math Expressions Evaluator

  Library that evals complex mathematical expressions into values

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• How does this circle collision detection math work?

  - by Griffin

  I'm going through the wildbunny blog to learn about collision detection. I'm confused about how the vectors he's talking about come into play. Here's the part that confuses me: p = ||A-B|| – (r1+r2) The two spheres are penetrating by distance p. We would also like the penetration vector so that we can correct the penetration once we discover it. This is the vector that moves both circles to the point where they just touch, correcting the penetration. Importantly it is not only just a vector that does this, it is the only vector which corrects the penetration by moving the minimum amount. This is important because we only want to correct the error, not introduce more by moving too much when we correct, or too little. N = (A-B) / ||A-B|| P = N*p Here we have calculated the normalised vector N between the two centres and the penetration vector P by multiplying our unit direction by the penetration distance. I understand that p is the distance by which the circles penetrate, but I don't get what exactly N and P are. It seems to me N is just the coordinates of the 3rd point of the right trianlge formed by point A and B (A-B) then being divided by the hypotenuse of that triangle or distance between A and B (||A-B||). What's the significance of this? Also, what is the penetration vector used for? It seems to me like a movement that one of the circles would perform to get un-penetrated.

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• C# Collision Math Help

  - by user36037

  I am making my own collision detection in MonoGame. I have a PolyLine class That has a property to return the normal of that PolyLine instance. I have a ConvexPolySprite class that has a List LineSegments. I hav a CircleSprite class that has a Center Property and a Radius Property. I am using a static class for the collision detection method. I am testing it on a single line segment. Vector2(200,0) = Vector2(300, 200) The problem is it detects the collision anywhere along the path of line out into space. I cannot figure out why. Thanks in advance; public class PolyLine { //--------------------------------------------------------------------------------------------------------------------------- // Class Properties /// <summary> /// Property for the upper left-hand corner of the owner of this instance /// </summary> public Vector2 ParentPosition { get; set; } /// <summary> /// Relative start point of the line segment /// </summary> public Vector2 RelativeStartPoint { get; set; } /// <summary> /// Relative end point of the line segment /// </summary> public Vector2 RelativeEndPoint { get; set; } /// <summary> /// Property that gets the absolute position of the starting point of the line segment /// </summary> public Vector2 AbsoluteStartPoint { get { return ParentPosition + RelativeStartPoint; } }//end of AbsoluteStartPoint /// <summary> /// Gets the absolute position of the end point of the line segment /// </summary> public Vector2 AbsoluteEndPoint { get { return ParentPosition + RelativeEndPoint; } }//end of AbsoluteEndPoint public Vector2 NormalizedLeftNormal { get { Vector2 P = AbsoluteEndPoint - AbsoluteStartPoint; P.Normalize(); float x = P.X; float y = P.Y; return new Vector2(-y, x); } }//end of NormalizedLeftNormal //--------------------------------------------------------------------------------------------------------------------------- // Class Constructors /// <summary> /// Sole ctor /// </summary> /// <param name="parentPosition"></param> /// <param name="relStart"></param> /// <param name="relEnd"></param> public PolyLine(Vector2 parentPosition, Vector2 relStart, Vector2 relEnd) { ParentPosition = parentPosition; RelativeEndPoint = relEnd; RelativeStartPoint = relStart; }//end of ctor }//end of PolyLine class public static bool Collided(CircleSprite circle, ConvexPolygonSprite poly) { var distance = Vector2.Dot(circle.Position - poly.LineSegments[0].AbsoluteEndPoint, poly.LineSegments[0].NormalizedLeftNormal) + circle.Radius; if (distance <= 0) { return false; } else { return true; } }//end of collided

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• Create Math Game with PHP, Ajax, Jquery

  - by Sambucasun

  I am developing a website where user can create their own game which can be joined by other users as well. It's a simple maths game which will shoot equations based on time or count specified. I want that moment user create a game, it will be listed in "current Games" section. Other users can check out the list and select the game to join. After game is created, creater should have a screen which should be having his name with display pic. Now gradually as others start joining the game, list should updated automatically. Once enough users are there i will start the game. The same list should be displayed to other users who join the game. Once game is over all will be displayed a summary list. I have gone through couple of threads but could not get clear idea. Do I need to use comet or other technology to create such game or simple PHP, Ajax or Jquery will suffice ? Also I want my website should be mobile compatible so i am designing it in html5. If i create this game using just Ajax then will there be any performance issue while playing through mobile. I am not much experienced so just need guidance for what should be appropriate or use for my requirement.

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• Help on understanding JS

  - by Anonymous

  I have thos piece of code: Math&&Math.random?Math.floor(Math.random()*10000000000000):Date.getTime(); And as far as i know && is logic operator for AND, so im trying to convert this into PHP and this is where i got: intval(floor(time()/10800000)%10+(rand()?floor(rand()*10000000000000):time())) The problem is that i can't understand the first part Math&& Can anyone help with this one cause i always get negative result, when i should get positive (probably the logic rand-time is not working in my php example)

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• Make The Web Fast - The HAR Show: Capturing and Analyzing performance data with HTTP Archive format

  Make The Web Fast - The HAR Show: Capturing and Analyzing performance data with HTTP Archive format Need a flexible format to record, export, and analyze network performance data? Well, that's exactly what the HTTP Archive format (HAR) is designed to do! Even better, did you know that Chrome DevTools supports it? In this episode we'll take a deep dive into the format (as you'll see, its very simple), and explore the many different ways it can help you capture and analyze your sites performance. Join +Ilya Grigorik and +Peter Lubbers to find out how to capture HAR network traces in Chrome, visualize the data via an online tool, share the reports with your clients and coworkers, automate the logging and capture of HAR data for your build scripts, and even adapt it to server-side analysis use cases! Yes, a rapid fire session of awesome demos - see you there. From: GoogleDevelopers Views: 0 6 ratings Time: 00:00 More in Science & Technology

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• How is this site so fast?

  - by user8628

  how is the website http://dftba.com/ so fast? when i click a link it loads right then? what makes it work like this? how do i make it work like this on my site? some of the objects on the site are being hosted by a website called ecogeek-cdn.net? who is this company and why do they host the images of this site? i have been looking into this site some time because i want this site to be like mine site they site use Apache they site use Python (when asked the developer told me this) they site use jquery and jqueryui they site is custom built not using wordpress they site is ownedhosted by liquidweb they site gets a million users a month they site launched in january they site uses cpanel they site does not have SSH or FTP (i tried to connect but it denied me all) they does have SSH and FTP but only allowed by their addresses Please; my english is not as good as yours

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• Asciifi Is a Lightening Fast Web-Based ASCII Converter

  - by Jason Fitzpatrick

  If you have a hankering from some old-school ASCII artwork, Asciifi is a free and lightening fast HTML5 ASCII converter. Despite the simplicity of ASCII images (pictures created not out of a grid of colored pixels like a standard digital photograph but out of a grid of text characters) many ASCII converters are rather slow. Asciifi speeds up the process by rendering your images on the fly with a snappy HTML5-based converter. Visit the site, drag and drop your image, and almost instantaneously you’ll see the results. The output can be further tweaked by adjusting the line width and the character set used. Hit up the link below to take it for a test drive. Asciifi [via Digital Inspiration] HTG Explains: Understanding Routers, Switches, and Network Hardware How to Use Offline Files in Windows to Cache Your Networked Files Offline How to See What Web Sites Your Computer is Secretly Connecting To

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• Web.NET is Closing Fast

  - by Chris Massey

  The voting for sessions has now closed, and sadly only half of the potential sessions could make it through. On the plus side, the sessions that floated to the top look great and, with the votes in, Simone and Ugo have moved right along and created a draft agenda to whet our appetites. Take a look, and let them know what you think. I’d also strongly recommend that you get ready to grab your tickets when they become available next week (specifically, September 18th), as places are going to be snapped up fast. In case you need a reminder as to why Web.NET is worth your time: Complete focus on web development Awesome sessions All-night hackathon Free (although I urge you to make a donation to help Simone and Ugo create the best possible event) Put October 20th in your calendar, and start packing. I’ve already booked my flights, and am perusing the list of hotels while I eat my lunch. Bonus Material There will be a full day of RavenDB training on Monday the 22nd of October, run by Ayende himself, and attending Web.NET will get you a 30% discount on the cost of the session.

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• GNOME 3.4 released, with smooth & fast magnification

  - by Peter Korn

  The GNOME community released GNOME 3.4 today. This release contains several new accessibility features, along with a new set of custom high-contrast icons which improve the user experience for users needing improved contrast. This release also makes available the AEGIS-funded GNOME Shell Magnifier. This magnifier leverages the powerful graphics functionality built into all modern video cards for smooth and fast magnification in GNOME. You can watch a video of that magnifier (with the previous version of the preference dialog), which shows all of the features now available in GNOME 3.4. This includes full/partial screen magnification, a magnifier lens, full or partial mouse cross hairs with translucency, and several mouse tracking modes. Future improvements planned for GNOME 3.6 include focus & caret tracking, and a variety of color/contrast controls.

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• Fast Track Data Warehouse 3.0 Reference Guide

  - by jchang

  Microsoft just release Fast Track Data Warehouse 3.0 Reference Guide version. The new changes are increased memory recommendation and the disks per RAID group change from 2-disk RAID 1 to 4-Disk RAID 10. Memory The earlier FTDW reference architecture cited 4GB memory per core. There was no rational behind this, but it was felt some rule was better than no rule. The new FTDW RG correctly cites the rational that more memory helps keep hash join intermediate results and sort operations in memory. 4-Disk...(read more)

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• Google I/O 2012 - Fast UIs for the Cross-Device Web

  Google I/O 2012 - Fast UIs for the Cross-Device Web Boris Smus One of the great features of the modern web is that sites work on any device with a browser. This session will focus on creating UIs for the cross-device web. We will cover building web sites that support multiple device form factors (responsive and non-responsive approaches), discuss single page sites and some of the layout features in modern mobile browsers, and do a deep dive into multi-touch input on the web. Finally, we'll show some of the awesome new mobile debugging tools in Chrome and Chrome for Android. For all I/O 2012 sessions, go to developers.google.com From: GoogleDevelopers Views: 105 3 ratings Time: 49:31 More in Science & Technology

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• Searching for fast skeletal animation algorithm

  - by igf

  Is it theoretically possible to dynamicaly animate scene with 100-150 400 poly characters meshes on high-end GL ES 2.0 mobile devices or i definetley should use prerendered keyframe animation? Scene have only one light source and precalculated shadow maps. View from top like in Warcraft 3. No any other meshes or objects. 2d collision detecting between objects calculated via spatial hashing. It can be any other algorithm besides ragdoll, but it must supply fast and simple skeletal animation for frame with 100+ low poly meshes for each mesh. Any ideas?

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• Fast lighting with multiple lights

  - by codymanix

  How can I implement fast lighting with multiple lights? I don't want to restrain the player, he can place an unlimited number and possibly overlapping (point) lights into the level. The problem is that shaders which contain dynamic loops which would be necessary to calculate the lighting tend to be very slow. I had the idea that if it could be possible at compiletime to compile a shader n times where n is the number of lights. If the number n is known at compiletime, the loops can be unrolled automatically. Is this possible to generate n versions of the same shader with just a different number of lights? At runtime I could then decide which shader to use for which part of the level.

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• cpu temperature imrpoves very fast

  - by myildirim

  Last few days i found out that when i click google chrome and the open it my laptop starts being angry.That's fans are working hardly and i can not touch the mousepad because of heating.I use Ubuntu 11.10 on my Toshiba A350-22z laptop and monitor cpu and harddrive temperature.Both cores reached 104 Celcius and i read somewhere "if your processor reaches 105Celcius it harms itself".I cleaned inside of laptop a year ago but there is a point : until wheather becomes about 20Celcius there was no problem.I know hardware cleaning is the best solution but how can i solve with another way ? I think problem is about outside's hot wheather.Is there anybody that has the same problem.In addition to Google Chrome i realized that when i open online video the processor temperature increas very fast.

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• Fast lighting with multple lights

  - by codymanix

  How can I implement fast lighting with multiple lights? I don't want to restrain the player, he can place an unlimited number and possibly overlapping (point) lights into the level. The problem is that shaders which contain dynamic loops which would be necessary to calculate the lighting tend to be very slow. I had the idea that if it could be possible at compiletime to compile a shader n times where n is the number of lights. If the number n is known at compiletime, the loops can be unrolled automatically. Is this possible to generate n versions of the same shader with just a different number of lights? At runtime I could then decide which shader to use for which part of the level.

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• Fast lookup for organization hierarchy

  - by Élodie Petit

  I need a way to implement a fast lookup algorithm / system to find users very quickly in a multi-level department and multi-level employee/manager relation organization structure. Departments can have any level of departments and users directly connected to departments. User are connected to departments and other users at the same time. What would be the best approach to implement such a system? There will be approximately 2000 users and 30 departments. Is there a good way to hold all of this information on memory?

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• Exciting DBA and BI role in London for fast growing startup

  - by simonsabin

  One of my clients is looking for a DBA and a BI developer. They are a very exciting dotcom company with cutting edge technology and are growing fast  A bit older than a startup but they still have that feel about them. They are based in North London and are a very nice company to work for, flexible hours, working from home. Plus they are willing to pay for the right candidate. There is at least 1 DBA and 1 BI role going. If you are interested then let me know http://sqlblogcasts.com/blogs/simons...(read more)

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• Fast language for problem solving? [closed]

  - by Friend of Kim

  I learned PHP to make websites. After some years I've started using programming for solving what is difficult tasks for my level. Now I want to make a program that solves equations. (I want to write it myself, not use an API. Because I'm doing this for the sake of the challenge, not for the result..) Because of this, I'm going to learn a new and faster/better language. It's going to be C++, Java, Python or C#. What are the benefits of each language, and which language is best for speed compared to speed of writing and readability? Using C would be lightning fast, but the lack of OO is making for more complex code and reduces the readability, for example..

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• how to play MP3 files at fast speed

  - by Anil

  I have MP3 file and the contents are continuous and slow. Is there any tool, which converts them to fast speed. I am aware of the fact that with VLC, i can play fast. But, the problem is every time i have to fix the speed of the player. The Question is, i dont want to manipulate/tweak every time i play the file. I wish to have permanent solution to play the slow playing MP3 files to play fast (some thing like saving the file with fast speed etc).

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• How to tell if leaving iOS app entered foreground from fast-app switching or manually?

  - by JPK

  Is there a way to tell if an iOS app enters the foreground from fast-app switching or manually? I need to know by the time applicationWillEnterForeground is called, so some specific code can be executed (or not executed) depending on the condition in which the app entered the foreground. EDIT: It turned out that this was more of a design issue for me. I moved my code to applicationDidBecomeActive. I also added a BOOL property to the appDelegate called fastAppSwitching (probably the wrong name for it). I set this to YES in application:handleOpenURL and application:openURL:sourceApplication:annotation. Then I added the following code to application:didFinishLaunchingWithOptions: if (launchOptions) { self.fastAppSwitching = YES; } else { self.fastAppSwitching = NO; } In applicationDidBecomeActive, I used the following code: if (fastAppSwitching == YES) { self.fastAppSwitching = NO; //stop, don't go any further } else { ... } EDIT2: MaxGabriel makes a good point below: "Just a warning to others taking the solution described here, applicationDidBecomeActive: is called when the user e.g. ignores a phone call or text message, unlike applicationWillEnterForeground". This is actually also true for in-app purchases and Facebook in-app authorization (new in iOS 6). So, with some further testing, this is the current solution: Add a new Bool called passedThroughWillEnterForeground. In applicationWillResignActive: self.passedThroughWillEnterForeground = NO; In applicationDidEnterBackground: self.passedThroughWillEnterForeground = NO; In applicationWillEnterForeground: self.passedThroughWillEnterForeground = YES; In applicationDidBecomeActive: if (passedThroughWillEnterForeground) { //we are NOT returning from 6.0 (in-app) authorization dialog or in-app purchase dialog, etc //do nothing with this BOOL - just reset it self.passedThroughWillEnterForeground = NO; } else { //we ARE returning from 6.0 (in-app) authorization dialog or in-app purchase dialog - IE //This is the same as fast-app switching in our book, so let's keep it simple and use this to set that self.fastAppSwitching = YES; } if (fastAppSwitching == YES) { self.fastAppSwitching = NO; } else { ... } EDIT3: I think we also need a bool to tell if app was launched from terminated.

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• My raycaster is putting out strange results, how do I fix it?

  - by JamesK89

  I'm working on a raycaster in ActionScript 3.0 for the fun of it, and as a learning experience. I've got it up and running and its displaying me output as expected however I'm getting this strange bug where rays go through corners of blocks and the edges of blocks appear through walls. Maybe somebody with more experience can point out what I'm doing wrong or maybe a fresh pair of eyes can spot a tiny bug I haven't noticed. Thank you so much for your help! Screenshots: http://i55.tinypic.com/25koebm.jpg http://i51.tinypic.com/zx5jq9.jpg Relevant code: function drawScene() { rays.graphics.clear(); rays.graphics.lineStyle(1, rgba(0x00,0x66,0x00)); var halfFov = (player.fov/2); var numRays:int = ( stage.stageWidth / COLUMN_SIZE ); var prjDist = ( stage.stageWidth / 2 ) / Math.tan(toRad( halfFov )); var angStep = ( player.fov / numRays ); for( var i:int = 0; i < numRays; i++ ) { var rAng = ( ( player.angle - halfFov ) + ( angStep * i ) ) % 360; if( rAng < 0 ) rAng += 360; var ray:Object = castRay(player.position, rAng); drawRaySlice(i*COLUMN_SIZE, prjDist, player.angle, ray); } } function drawRaySlice(sx:int, prjDist, angle, ray:Object) { if( ray.distance >= MAX_DIST ) return; var height:int = int(( TILE_SIZE / (ray.distance * Math.cos(toRad(angle-ray.angle))) ) * prjDist); if( !height ) return; var yTop = int(( stage.stageHeight / 2 ) - ( height / 2 )); if( yTop < 0 ) yTop = 0; var yBot = int(( stage.stageHeight / 2 ) + ( height / 2 )); if( yBot > stage.stageHeight ) yBot = stage.stageHeight; rays.graphics.moveTo( (ray.origin.x / TILE_SIZE) * MINI_SIZE, (ray.origin.y / TILE_SIZE) * MINI_SIZE ); rays.graphics.lineTo( (ray.hit.x / TILE_SIZE) * MINI_SIZE, (ray.hit.y / TILE_SIZE) * MINI_SIZE ); for( var x:int = 0; x < COLUMN_SIZE; x++ ) { for( var y:int = yTop; y < yBot; y++ ) { buffer.setPixel(sx+x, y, clrTable[ray.tile-1] >> ( ray.horz ? 1 : 0 )); } } } function castRay(origin:Point, angle):Object { // Return values var rTexel = 0; var rHorz = false; var rTile = 0; var rDist = MAX_DIST + 1; var rMap:Point = new Point(); var rHit:Point = new Point(); // Ray angle and slope var ra = toRad(angle) % ANGLE_360; if( ra < ANGLE_0 ) ra += ANGLE_360; var rs = Math.tan(ra); var rUp = ( ra > ANGLE_0 && ra < ANGLE_180 ); var rRight = ( ra < ANGLE_90 || ra > ANGLE_270 ); // Ray position var rx = 0; var ry = 0; // Ray step values var xa = 0; var ya = 0; // Ray position, in map coordinates var mx:int = 0; var my:int = 0; var mt:int = 0; // Distance var dx = 0; var dy = 0; var ds = MAX_DIST + 1; // Horizontal intersection if( ra != ANGLE_180 && ra != ANGLE_0 && ra != ANGLE_360 ) { ya = ( rUp ? TILE_SIZE : -TILE_SIZE ); xa = ya / rs; ry = int( origin.y / TILE_SIZE ) * ( TILE_SIZE ) + ( rUp ? TILE_SIZE : -1 ); rx = origin.x + ( ry - origin.y ) / rs; mx = 0; my = 0; while( mx >= 0 && my >= 0 && mx < world.size.x && my < world.size.y ) { mx = int( rx / TILE_SIZE ); my = int( ry / TILE_SIZE ); mt = getMapTile(mx,my); if( mt > 0 && mt < 9 ) { dx = rx - origin.x; dy = ry - origin.y; ds = ( dx * dx ) + ( dy * dy ); if( rDist >= MAX_DIST || ds < rDist ) { rDist = ds; rTile = mt; rMap.x = mx; rMap.y = my; rHit.x = rx; rHit.y = ry; rHorz = true; rTexel = int(rx % TILE_SIZE) } break; } rx += xa; ry += ya; } } // Vertical intersection if( ra != ANGLE_90 && ra != ANGLE_270 ) { xa = ( rRight ? TILE_SIZE : -TILE_SIZE ); ya = xa * rs; rx = int( origin.x / TILE_SIZE ) * ( TILE_SIZE ) + ( rRight ? TILE_SIZE : -1 ); ry = origin.y + ( rx - origin.x ) * rs; mx = 0; my = 0; while( mx >= 0 && my >= 0 && mx < world.size.x && my < world.size.y ) { mx = int( rx / TILE_SIZE ); my = int( ry / TILE_SIZE ); mt = getMapTile(mx,my); if( mt > 0 && mt < 9 ) { dx = rx - origin.x; dy = ry - origin.y; ds = ( dx * dx ) + ( dy * dy ); if( rDist >= MAX_DIST || ds < rDist ) { rDist = ds; rTile = mt; rMap.x = mx; rMap.y = my; rHit.x = rx; rHit.y = ry; rHorz = false; rTexel = int(ry % TILE_SIZE); } break; } rx += xa; ry += ya; } } return { angle: angle, distance: Math.sqrt(rDist), hit: rHit, map: rMap, tile: rTile, horz: rHorz, origin: origin, texel: rTexel }; }

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• Complex.pm taking up a lot of time

  - by synapz

  While trying to profile my perl program, I find that Complex.pm is taking up a lot of time with what looks like some kind of warning. Also, my code shouldn't have any complex numbers being generated or used, so I am not sure what it is doing in Complex.pm, anyway. Here's the FastProf output for the most expensive lines: /usr/lib/perl5/5.8.8/Math/Complex.pm:182 1.55480 276232: _cannot_make("real part", $re) unless $re =~ /^$gre$/; /usr/lib/perl5/5.8.8/Math/Complex.pm:310 1.01132 453641: sub cartesian {$_[0]->{c_dirty} ? /usr/lib/perl5/5.8.8/Math/Complex.pm:315 0.97497 562188: sub set_cartesian { $_[0]->{p_dirty}++; $_[0]->{c_dirty} = 0; /usr/lib/perl5/5.8.8/Math/Complex.pm:189 0.86302 276232: return $self; /usr/lib/perl5/5.8.8/Math/Complex.pm:1332 0.85628 293660: $self->{display_format} = { %display_format }; /usr/lib/perl5/5.8.8/Math/Complex.pm:185 0.81529 276232: _cannot_make("imaginary part", $im) unless $im =~ /^$gre$/; /usr/lib/perl5/5.8.8/Math/Complex.pm:1316 0.78749 293660: my %display_format = %DISPLAY_FORMAT; /usr/lib/perl5/5.8.8/Math/Complex.pm:1335 0.69534 293660: %{$self->{display_format}} : /usr/lib/perl5/5.8.8/Math/Complex.pm:186 0.66697 276232: $self->set_cartesian([$re, $im ]); /usr/lib/perl5/5.8.8/Math/Complex.pm:170 0.62790 276232: my $self = bless {}, shift; /usr/lib/perl5/5.8.8/Math/Complex.pm:172 0.56733 276232: if (@_ == 0) { /usr/lib/perl5/5.8.8/Math/Complex.pm:316 0.53179 281094: $_[0]->{'cartesian'} = $_[1] } /usr/lib/perl5/5.8.8/Math/Complex.pm:1324 0.48768 293660: if (@_ == 1) { /usr/lib/perl5/5.8.8/Math/Complex.pm:1319 0.44835 293660: if (exists $self->{display_format}) { /usr/lib/perl5/5.8.8/Math/Complex.pm:1318 0.40355 293660: if (ref $self) { # Called as an object method /usr/lib/perl5/5.8.8/Math/Complex.pm:187 0.39950 276232: $self->display_format('cartesian'); /usr/lib/perl5/5.8.8/Math/Complex.pm:1315 0.39312 293660: my $self = shift; /usr/lib/perl5/5.8.8/Math/Complex.pm:1331 0.38087 293660: if (ref $self) { # Called as an object method /usr/lib/perl5/5.8.8/Math/Complex.pm:184 0.35171 276232: $im ||= 0; /usr/lib/perl5/5.8.8/Math/Complex.pm:181 0.34145 276232: if (defined $re) { /usr/lib/perl5/5.8.8/Math/Complex.pm:171 0.33492 276232: my ($re, $im); /usr/lib/perl5/5.8.8/Math/Complex.pm:390 0.20658 128280: my ($z1, $z2, $regular) = @_; /usr/lib/perl5/5.8.8/Math/Complex.pm:391 0.20631 128280: if ($z1->{p_dirty} == 0 and ref $z2 and $z2->{p_dirty} == 0) { Thanks for any help!

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• Why does the BigFraction class in the Apache-Commons-Math library return incorrect division results?

  - by Timothy Lee Russell

  In the spirit of using existing, tested and stable libraries of code, I started using the Apache-Commons-Math library and its BigFraction class to perform some rational calculations for an Android app I'm writing called RationalCalc. It works great for every task that I have thrown at it, except for one nagging problem. When dividing certain BigFraction values, I am getting incorrect results. If I create a BigFraction with the inverse of the divisor and multiply instead, I get the same incorrect answer but perhaps that is what the library is doing internally anyway. Does anyone know what I am doing wrong? The division works correctly with a BigFraction of 2.5 but not 2.51, 2.49, etc... // *** incorrect! *** BigFraction one = new BigFraction(1.524); //one: 1715871458028159 / 1125899906842624 BigFraction two = new BigFraction(2.51); //two: 1413004383087493 / 562949953421312 BigFraction three = one.divide(two); //three: 0 Log.i("solve", three.toString()); //should be 0.607171315 ?? //returns 0 // *** correct! **** BigFraction four = new BigFraction(1.524); //four: 1715871458028159 / 1125899906842624 BigFraction five = new BigFraction(2.5); //five: 5 / 2 BigFraction six = four.divide(five); //six: 1715871458028159 / 2814749767106560 Log.i("solve", six.toString()); //should be 0.6096 ?? //returns 0.6096

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• Getting a handle on GIS math, where do I start?

  - by Joshua

  I am in charge of a program that is used to create a set of nodes and paths for consumption by an autonomous ground vehicle. The program keeps track of the locations of all items in its map by indicating the item's position as being x meters north and y meters east of an origin point of 0,0. In the real world, the vehicle knows the location of the origin's lat and long, as it is determined by a dgps system and is accurate down to a couple centimeters. My program is ignorant of any lat long coordinates. It is one of my goals to modify the program to keep track of lat long coords of items in addition to an origin point and items' x,y position in relation to that origin. At first blush, it seems that I am going to modify the program to allow the lat long coords of the origin to be passed in, and after that I desire that the program will automatically calculate the lat long of every item currently in a map. From what I've researched so far, I believe that I will need to figure out the math behind converting to lat long coords from a UTM like projection where I specify the origin points and meridians etc as opposed to whatever is defined already for UTM. I've come to ask of you GIS programmers, am I on the right track? It seems to me like there is so much to wrap ones head around, and I'm not sure if the answer isn't something as simple as, "oh yea theres a conversion from meters to lat long, here" Currently, due to the nature of DGPS, the system really doesn't need to care about locations more than oh, what... 40 km? radius away from the origin. Given this, and the fact that I need to make sure that the error on my coordinates is not greater than .5 meters, do I need anything more complex than a simple lat/long to meters conversion constant? I'm knee deep in materials here. I could use some pointers about what concepts to research. Thanks much!

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