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• Inverting matrix then decomposing gives different quaternion than decomposing then inverting the quat

  - by Fraser

  I'm getting different signs when I convert a matrix to quaternion and invert that, versus when I invert a matrix and then get the quaternion from it: Quaternion a = Quaternion.Invert(getRotation(m)); Quaternion b = getRotation(Matrix.Invert(m)); I would expect a and b to be identical (or inverses of each other). However, it looks like q1 = (x, y, -z, -w) while q2 = (-x, -y, w, z). In other words, the Z and W components have been switched for some reason. Note: getRotation() decomposes the transform matrix and returns just the rotation part of it (I've tried normalizing the result; it does nothing). The matrix m is a complete transform matrix and contains a translation (and possibly a scale) as well as a rotation. I'm using D3DXMatrixDecompose to do the actual decomposition.

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• Missing z-axis rotation for transforming between two vectors

  - by Steve Baughman

  I'm trying to rotate a cube so that it's facing up, but am getting hung up on the final implementation details. It now reliably will rotate the x,y axis to the correct side, but the z-axis is never rotating (See photos of before and after rotation). When I'm using the code below I always get '0' for my rotationVector.z. What am I missing here? // Define lookAt vector lookAtVector = GLKVector3Make(0,0,1); // Define axes vectors axes[0] = GLKVector3Make(0,0,1); axes[1] = GLKVector3Make(-1,0,0); axes[2] = GLKVector3Make(0,1,0); axes[3] = GLKVector3Make(1,0,0); axes[4] = GLKVector3Make(0,-1,0); axes[5] = GLKVector3Make(0,0,-1); CGFloat highest_dot = -1.0; GLKVector3 closest_axis; for(int i = 0; i < 6; i++) { // multiply cube's axes by existing matrix GLKVector3 axis = GLKMatrix4MultiplyVector3(matrix, axes[i]); CGFloat dot = GLKVector3DotProduct(axis, lookAtVector); if(dot > highest_dot) { closest_axis = axis; highest_dot = dot; } } GLKVector3 rotationVector = GLKVector3CrossProduct(closest_axis, lookAtVector); // Get angle between vectors CGFloat angle = atan2(GLKVector3Length(rotationVector), GLKVector3DotProduct(closest_axis, lookAtVector)); // normalize the rotation vector rotationVector = GLKVector3Normalize(rotationVector); // Create transform CATransform3D rotationTransform = CATransform3DMakeRotation(angle, rotationVector.x, rotationVector.y, rotationVector.z); // add rotation transform to existing transformation baseTransform = CATransform3DConcat(baseTransform, rotationTransform); return baseTransform; Before 3d Rotation After 3d Rotation Implementation based on this post

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• Matrix multiplication - Scene Graphs

  - by bgarate

  I wrote a MatrixStack class in C# to use in a SceneGraph. So, to get the world matrix for an object I am suposed to use: WorldMatrix = ParentWorld * LocalTransform But, in fact, it only works as expected when I do the other way: WorldMatrix = LocalTransform * ParentWorld Mi code is: public class MatrixStack { Stack<Matrix> stack = new Stack<Matrix>(); Matrix result = Matrix.Identity; public void PushMatrix(Matrix matrix) { stack.Push(matrix); result = matrix * result; } public Matrix PopMatrix() { result = Matrix.Invert(stack.Peek()) * result; return stack.Pop(); } public Matrix Result { get { return result; } } public void Clear() { stack.Clear(); result = Matrix.Identity; } } Why it works this way and not the other? Thanks!

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• Rotate around the centre of the screen

  - by Dan Scott

  I want my camera to rotate around the centre of screen and I'm not sure how to achieve that. I have a rotation in the camera but I'm not sure what its rotating around. (I think it might be rotating around the position.X of camera, not sure) If you look at these two images: http://imgur.com/E9qoAM7,5qzyhGD#0 http://imgur.com/E9qoAM7,5qzyhGD#1 The first one shows how the camera is normally, and the second shows how I want the level to look when I would rotate the camera 90 degrees left or right. My camera: public class Camera { private Matrix transform; public Matrix Transform { get { return transform; } } private Vector2 position; public Vector2 Position { get { return position; } set { position = value; } } private float rotation; public float Rotation { get { return rotation; } set { rotation = value; } } private Viewport viewPort; public Camera(Viewport newView) { viewPort = newView; } public void Update(Player player) { position.X = player.PlayerPos.X + (player.PlayerRect.Width / 2) - viewPort.Width / 4; if (position.X < 0) position.X = 0; transform = Matrix.CreateTranslation(new Vector3(-position, 0)) * Matrix.CreateRotationZ(Rotation); if (Keyboard.GetState().IsKeyDown(Keys.D)) { rotation += 0.01f; } if (Keyboard.GetState().IsKeyDown(Keys.A)) { rotation -= 0.01f; } } } (I'm assuming you would need to rotate around the centre of the screen to achieve this)

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• What are the maths behind 'Raiden 2' purple laser?

  - by Aybe

  The path of the laser is affected by user input and enemies present on the screen. Here is a video, at 5:00 minutes the laser in question is shown : Raiden II (PS) - 1 Loop Clear - Part 2 UPDATE Here is a test using Inkscape, ship is at bottom, the first 4 enemies are targeted by the plasma. There seems to be a sort of pattern. I moved the ship first, then the handle from it to form a 45° angle, then while trying to fit the curve I found a pattern of parallel handles and continued so until I reached the last enemy. Update, 5/26/2012 : I started an XNA project using beziers, there is still some work needed, will update the question next week. Stay tuned ! Update : 5/30/2012 : It really seems that they are using Bézier curves, I think I will be able to replicate/imitate a plasma of such grade. There are two new topics I discovered since last time : Arc length, Runge's phenomenon, first one should help in having a linear movement possible over a Bézier curve, second should help in optimizing the number of vertices. Next time I will put a video so you can see the progress 8-)

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• Large sparse (stiff) ODE system needed for testing

  - by macydanim

  I hope this is the right place for this question. I have been working on a sparse stiff implicit ODE solver and have finished the code so far. I now tested the solver with the Van der Pol equation, and another stiff problem, which is of dimension 4. But to perform better tests I am searching for a bigger system. I'm thinking of the order N = 100...1000, if possible stiff and sparse. Does anybody have an example I could use? I really don't know where to search.

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• Typical Applications of Linear System Solver in Game Developemnt

  - by craftsman.don

  I am going to write a custom solver for linear system. I would like to survey the typical problems involved the linear system solving in games. So that I can custom optimization on these problems based on the shape of the matrix. currently I am focus on these problems: B-Spline editing (I use a linear solve to resolve the C0, C1, C2 continuity) Constraint in Simulation (especially Position-Constraint, cloth) Both of them are Banded Matrix. I want to hear about some other applications of a linear system in games. Thank you.

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• Logarithmic spacing of FFT bins

  - by Mykel Stone

  I'm trying to do the examples within the GameDev.net Beat Detection article ( http://archive.gamedev.net/archive/reference/programming/features/beatdetection/index.html ) I have no issue with performing a FFT and getting the frequency data and doing most of the article. I'm running into trouble though in the section 2.B, Enhancements and beat decision factors. in this section the author gives 3 equations numbered R10-R12 to be used to determine how many bins go into each subband: R10 - Linear increase of the width of the subband with its index R11 - We can choose for example the width of the first subband R12 - The sum of all the widths must not exceed 1024 He says the following in the article: "Once you have equations (R11) and (R12) it is fairly easy to extract 'a' and 'b', and thus to find the law of the 'wi'. This calculus of 'a' and 'b' must be made manually and 'a' and 'b' defined as constants in the source; indeed they do not vary during the song." However, I cannot seem to understand how these values are calculated...I'm probably missing something simple, but learning fourier analysis in a couple of weeks has left me Decimated-in-Mind and I cannot seem to see it.

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• Languages/Methods to Learn for Scientific Computing?:

  - by Zéychin

  I'm a second-semester Junior working towards a Computer Science degree with a Scientific Computing concentration and a Mathematics degree with a concentration on Applied Discrete Mathematics. So, number crunching and such rather than a bunch of regular expressions, interface design, and networking. I've found that I'm not learning new relevant languages from my coursework and am interested in what the community would recommend me to learn. I know as far as programming methods go, I need to learn more about parallelizing programs, but if there's anything else you can recommend, I would appreciate it. Here's a list of the languages with which I am very experienced (web technologies omitted as they barely apply here). Any recommendations for additional languages I should learn would be very much appreciated!: Java C C++ Fortran77/90/95 Haskell Python MATLAB

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• How can I make sense of the word "Functor" from a semantic standpoint?

  - by guillaume31

  When facing new programming jargon words, I first try to reason about them from an semantic and etymological standpoint when possible (that is, when they aren't obscure acronyms). For instance, you can get the beginning of a hint of what things like Polymorphism or even Monad are about with the help of a little Greek/Latin. At the very least, once you've learned the concept, the word itself appears to go along with it well. I guess that's part of why we name things names, to make mental representations and associations more fluent. I found Functor to be a tougher nut to crack. Not so much the C++ meaning -- an object that acts (-or) as a function (funct-), but the various functional meanings (in ML, Haskell) definitely left me puzzled. From the (mathematics) Functor Wikipedia article, it seems the word was borrowed from linguistics. I think I get what a "function word" or "functor" means in that context - a word that "makes function" as opposed to a word that "makes sense". But I can't really relate that to the notion of Functor in category theory, let alone functional programming. I imagined a Functor to be something that creates functions, or behaves like a function, or short for "functional constructor", but none of those seems to fit... How do experienced functional programmers reason about this ? Do they just need any label to put in front of a concept and be fine with it ? Generally speaking, isn't it partly why advanced functional programming is hard to grasp for mere mortals compared to, say, OO -- very abstract in that you can't relate it to anything familiar ? Note that I don't need a definition of Functor, only an explanation that would allow me to relate it to something more tangible, if there is any.

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• Are there any formalized/mathematical theories of software testing?

  - by Erik Allik

  Googling "software testing theory" only seems to give theories in the soft sense of the word; I have not been able to find anything that would classify as a theory in the mathematical, information theoretical or some other scientific field's sense. What I'm looking for is something that formalizes what testing is, the notions used, what a test case is, the feasibility of testing something, the practicality of testing something, the extent to which something should be tested, formal definition/explanation of code coverage, etc. UPDATE: Also, I'm not sure, intuitively, about the connection between formal verification and what I asked, but there's clearly some sort of connection.

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• Determining explosion radius damage - Circle to Rectangle 2D

  - by Paul Renton

  One of the Cocos2D games I am working on has circular explosion effects. These explosion effects need to deal a percentage of their set maximum damage to all game characters (represented by rectangular bounding boxes as the objects in question are tanks) within the explosion radius. So this boils down to circle to rectangle collision and how far away the circle's radius is from the closest rectangle edge. I took a stab at figuring this out last night, but I believe there may be a better way. In particular, I don't know the best way to determine what percentage of damage to apply based on the distance calculated. Note : All tank objects have an anchor point of (0,0) so position is according to bottom left corner of bounding box. Explosion point is the center point of the circular explosion. TankObject * tank = (TankObject*) gameSprite; float distanceFromExplosionCenter; // IMPORTANT :: All GameCharacter have an assumed (0,0) anchor if (explosionPoint.x < tank.position.x) { // Explosion to WEST of tank if (explosionPoint.y <= tank.position.y) { //Explosion SOUTHWEST distanceFromExplosionCenter = ccpDistance(explosionPoint, tank.position); } else if (explosionPoint.y >= (tank.position.y + tank.contentSize.height)) { // Explosion NORTHWEST distanceFromExplosionCenter = ccpDistance(explosionPoint, ccp(tank.position.x, tank.position.y + tank.contentSize.height)); } else { // Exp center's y is between bottom and top corner of rect distanceFromExplosionCenter = tank.position.x - explosionPoint.x; } // end if } else if (explosionPoint.x > (tank.position.x + tank.contentSize.width)) { // Explosion to EAST of tank if (explosionPoint.y <= tank.position.y) { //Explosion SOUTHEAST distanceFromExplosionCenter = ccpDistance(explosionPoint, ccp(tank.position.x + tank.contentSize.width, tank.position.y)); } else if (explosionPoint.y >= (tank.position.y + tank.contentSize.height)) { // Explosion NORTHEAST distanceFromExplosionCenter = ccpDistance(explosionPoint, ccp(tank.position.x + tank.contentSize.width, tank.position.y + tank.contentSize.height)); } else { // Exp center's y is between bottom and top corner of rect distanceFromExplosionCenter = explosionPoint.x - (tank.position.x + tank.contentSize.width); } // end if } else { // Tank is either north or south and is inbetween left and right corner of rect if (explosionPoint.y < tank.position.y) { // Explosion is South distanceFromExplosionCenter = tank.position.y - explosionPoint.y; } else { // Explosion is North distanceFromExplosionCenter = explosionPoint.y - (tank.position.y + tank.contentSize.height); } // end if } // end outer if if (distanceFromExplosionCenter < explosionRadius) { /* Collision :: Smaller distance larger the damage */ int damageToApply; if (self.directHit) { damageToApply = self.explosionMaxDamage + self.directHitBonusDamage; [tank takeDamageAndAdjustHealthBar:damageToApply]; CCLOG(@"Explsoion-> DIRECT HIT with total damage %d", damageToApply); } else { // TODO adjust this... turning out negative for some reason... damageToApply = (1 - (distanceFromExplosionCenter/explosionRadius) * explosionMaxDamage); [tank takeDamageAndAdjustHealthBar:damageToApply]; CCLOG(@"Explosion-> Non direct hit collision with tank"); CCLOG(@"Damage to apply is %d", damageToApply); } // end if } else { CCLOG(@"Explosion-> Explosion distance is larger than explosion radius"); } // end if } // end if Questions: 1) Can this circle to rect collision algorithm be done better? Do I have too many checks? 2) How to calculate the percentage based damage? My current method generates negative numbers occasionally and I don't understand why (Maybe I need more sleep!). But, in my if statement, I ask if distance < explosion radius. When control goes through, distance/radius must be < 1 right? So 1 - that intermediate calculation should not be negative. Appreciate any help/advice!

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• Physics timestep questions

  - by SSL

  I've got a projectile working perfectly using the code below: //initialised in loading screen 60 is the FPS - projectilEposition and velocity are Vector3 types gravity = new Vector3(0, -(float)9.81 / 60, 0); //called every frame projectilePosition += projectileVelocity; This seems to work fine but I've noticed in various projectile examples I've seen that the elapsedtime per update is taken into account. What's the difference between the two and how can I convert the above to take into account the elapsedtime? (I'm using XNA - do I use ElapsedTime.TotalSeconds or TotalMilliseconds)? Edit: Forgot to add my attempt at using elapsedtime, which seemed to break the physics: projectileVelocity.Y += -(float)((9.81 * gameTime.ElapsedGameTime.TotalSeconds * gameTime.ElapsedGameTime.TotalSeconds) * 0.5f); Thanks for the help

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• building a game for different resoulution phones

  - by Jason

  Hi, I am starting some tests for building a game on the android program. So far everything is working and seems nice. However I do not understand how to make sure my game looks correct on all phones as the all will have slightly different screen ratios (and even very different on some odd phones) What I am doing right now is making a view frustrum ( could also be ortho ) which I set to go from -ratio to +ratio ( as I have seen on many examples) however this causes my test shape to be stretched and sometimes cut off by the edge of the screen. I am tilting my phone to landscape to do my tests ( a bit extreame) but it should still render correctly if I have dome things right. Should I be scaling by some ratio before drawing or something? An example would be greatly apriciated PS I am doing a 2d game

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• Gödel, Escher, Bach - Gödel's string

  - by Brad Urani

  In the book Gödel, Escher, Bach: An Eternal Golden Braid by Douglas Hofstadter, the author gives us a representation of the precursor to Gödel's string (Gödel's string's uncle) as: ~Ea,a': (I don't have the book in front of me but I think that's right). All that remains to get Gödel's string is to plug the Gödel number for this string into the free variable a''. What I don't understand is how to get the Gödel number for the functions PROOF-PAIR and ARITHMOQUINE. I understand how to write these functions in a programming language like FlooP (from the book) and could even write them myself in C# or Java, but the scheme that Hofstadter defines for Gödel numbering only applies to TNT (which is just his own syntax for natural number theory) and I don't see any way to write a procedure in TNT since it doesn't have any loops, variable assignments etc. Am I missing the point? Perhaps Gödel's string is not something that can actually be printed, but rather a theoretical string that need not actually be defined? I thought it would be neat to write a computer program that actually prints Gödel's string, or Gödel's string encoded by Gödel numbering (yes, I realize it would have a gazillion digits) but it seems like doing so requires some kind of procedural language and a Gödel numbering system for that procedural language that isn't included in the book. Of course once you had that, you could write a program that plugs random numbers into variable "a" and run procedure PROOF-PAIR on it to test for theoromhood of Gödel's string. If you let it run for a trillion years you might find a derivation that proves Gödel's string.

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• convert orientation vec3 to a rotation matrix

  - by lapin

  I've got a normalized vec3 that represents an orientation. Each frame of animation, an object's orientation changes slightly, so I add a delta vector to the orientation vector and then normalize to find the new orientation. I'd like to convert the vec3 that represents an orientation into a rotation matrix that I can use to orient my object. If it helps, my object is a cone, and I'd like to rotate it about the pointy end, not from its center :) PS I know I should use quaternions because of the gimbal lock problem. If someone can explain quats too, that'd be great :)

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• Orthographic unit translation mismatch on grid (e.g. 64 pixels translates incorrectly)

  - by Justin Van Horne

  I am looking for some insight into a small problem with unit translations on a grid. Setup 512x448 window 64x64 grid gl_Position = projection * world * position; projection is defined by ortho(-w/2.0f, w/2.0f, -h/2.0f, h/2.0f); This is a textbook orthogonal projection function. world is defined by a fixed camera position at (0, 0) position is defined by the sprite's position. Problem In the screenshot below (1:1 scaling) the grid spacing is 64x64 and I am drawing the unit at (64, 64), however the unit draws roughly ~10px in the wrong position. I've tried uniform window dimensions to prevent any distortion on the pixel size, but now I am a bit lost in the proper way in providing a 1:1 pixel-to-world-unit projection. Anyhow, here are some quick images to aide in the problem. I decided to super-impose a bunch of the sprites at what the engine believes is 64x offsets. When this seemed off place, I went about and did the base case of 1 unit. Which seemed to line up as expected. The yellow shows a 1px difference in the movement. Vertices It would appear that the vertices going into the vertex shader are correct. For example, in reference to the first image the data looks like this in the VBO: x y x y ---------------------------- tl | 0.0 24.0 64.0 24.0 bl | 0.0 0.0 -> 64.0 0.0 tr | 16.0 0.0 80.0 0.0 br | 16.0 24.0 80.0 24.0 With that said, all I am left to believe is that I am munging up my actual projection. So, I am looking for any insight into maintaining the 1:1 pixel-to-world-unit projection.

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• Robust line of sight test on the inside of a polygon with tolerance

  - by David Gouveia

  Foreword This is a followup to this question and the main problem I'm trying to solve. My current solution is an hack which involves inflating the polygon, and doing most calculations on the inflated polygon instead. My goal is to remove this step completely, and correctly solve the problem with calculations only. Problem Given a concave polygon and treating all of its edges as if they were walls in a level, determine whether two points A and B are in line of sight of each other, while accounting for some degree of floating point errors. I'm currently basing my solution on a series of line-segment interection tests. In other words: If any of the end points are outside the polygon, they are not in line of sight. If both end points are inside the polygon, and the line segment from A to B crosses any of the edges from the polygon, then they are not in line of sight. If both end points are inside the polygon, and the line segment from A to B does not cross any of the edges from the polygon, then they are in line of sight. But the problem is dealing correctly with all the edge cases. In particular, it must be able to deal with all the situations depicted below, where red lines are examples that should be rejected, and green lines are examples that should be accepted. I probably missed a few other situations, such as when the line segment from A to B is colinear with an edge, but one of the end points is outside the polygon. One point of particular interest is the difference between 1 and 9. In both cases, both end points are vertices of the polygon, and there are no edges being intersected, but 1 should be rejected while 9 should be accepted. How to distinguish these two? I could check some middle point within the segment to see if it falls inside or not, but it's easy to come up with situations in which it would fail. Point 7 was also pretty tricky and I had to to treat it as a special case, which checks if two points are adjacent vertices of the polygon directly. But there are also other chances of line segments being col linear with the edges of the polygon, and I'm still not entirely sure how I should handle those cases. Is there any well known solution to this problem?

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• Mandelbrot set not displaying properly

  - by brainydexter

  I am trying to render mandelbrot set using glsl. I'm not sure why its not rendering the correct shape. Does the mandelbrot calculation require values to be within a range for the (x,y) [ or (real, imag) ] ? Here is a screenshot: I render a quad as follows: float w2 = 6; float h2 = 5; glBegin(GL_QUADS); glVertex3f(-w2, h2, 0.0); glVertex3f(-w2, -h2, 0.0); glVertex3f(w2, -h2, 0.0); glVertex3f(w2, h2, 0.0); glEnd(); My vertex shader: varying vec3 Position; void main(void) { Position = gl_Vertex.xyz; gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex; } My fragment shader (where all the meat is): uniform float MAXITERATIONS; varying vec3 Position; void main (void) { float zoom = 1.0; float centerX = 0.0; float centerY = 0.0; float real = Position.x * zoom + centerX; float imag = Position.y * zoom + centerY; float r2 = 0.0; float iter; for(iter = 0.0; iter < MAXITERATIONS && r2 < 4.0; ++iter) { float tempreal = real; real = (tempreal * tempreal) + (imag * imag); imag = 2.0 * real * imag; r2 = (real * real) + (imag * imag); } vec3 color; if(r2 < 4.0) color = vec3(1.0); else color = vec3( iter / MAXITERATIONS ); gl_FragColor = vec4(color, 1.0); }

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• What resources are there for facial recognition

  - by Zintinio

  I'm interested in learning the theory behind facial recognition software so that I can hopefully implement it in the future. Not just face tracking, but being able to recognize individuals. What papers, books, libraries, or source is available so that I can learn more about the subject? I have found libface which seems to use eigenfaces for recognition. If there are any practitioners out there, please share any information that you can.

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• Calculating the position of an object with regards to current position using OpenGL like matrices

  - by spartan2417

  i have a 1st person camera that collides with walls, i also have a small sphere in front of my camera denoted by the camera position plus the distance ahead. I cannot get the postion of the sphere but i have the position of my camera. e.g. i need to find the position of the point or at the very least find away of calculating the position using the camera positions. code: static Float P_z = 0; P_z = -15; PushMatrix(); LoadMatrix(&Inv); Material(SCEGU_AMBIENT, 0x00000066); TranslateXYZ(0,0,P_z); ScaleXYZ(0.1f,0.1f,0.1f); pointer.Render(); PopMatrix(); where Inv is the camera positions (Inv.w.x,Inv.w.z), pointer is the sphere.

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• How can calculus and linear algebra be useful to a system programmer?

  - by Victor

  I found a website saying that calculus and linear algebra are necessary for System Programming. System Programming, as far as I know, is about osdev, drivers, utilities and so on. I just can't figure out how calculus and linear algebra can be helpful on that. I know that calculus has several applications in science, but in this particular field of programming I just can't imagine how calculus can be so important. The information was on this site: http://www.wikihow.com/Become-a-Programmer Edit: Some answers here are explaining about algorithm complexity and optimization. When I made this question I was trying to be more specific about the area of System's Programming. Algorithm complexity and optimization can be applied to any area of programming not just System's Programming. That may be why I wasn't able to came up with such thinking at the time of the question.

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• Has programming ruined your perception of round numbers?

  - by Jon Purdy

  Most of the world works in base 10 nowadays, but as programmers working on binary systems, we constantly find ourselves working with powers of 2. While most people consider integer multiples of powers of 10 "nice and round" and somehow aesthetically superior, I found early on in my programming adventures that multiples of powers of 2 feel much more intuitively round to me: fewer factors, of course. I'm much more likely to lay out a Web site using, say, 8- or 16-pixel margins rather than 10 or 20, and when someone remarks that 128 is an insanely arbitrary number of ounces to be in a gallon, I have to smile a little inside at how, just perhaps, the U.S. system might be superior to metric in one small way. I'm just curious: has programming ruined (read: altered) your perception of the roundness of a number?

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• Equation solver project

  - by Victor Barbu

  I would like to start a project destinated to students. My application has to solve any kind of equation, passed by the user as a string, exactly like in Matlab solve function. How shluld I do this? What programming language is the best for this purpose? Thanks in advance. P.S This is a screenshot made in Matlab. This is how I would like the user to insert and receive the answer: Another example:

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• Need help with a complex 3d scene (using Ogre and bullet)

  - by Matthias

  In my setup there is a box with a hole on one side, and a freely movable "stick" (or bar, tube). This stick can be inserted/moved through the hole into the box. This hole is exactly as wide as the diameter of the stick. In reality, when you would now hold the end of the stick in your hand and move the hand left/right or up/down, the other end of the stick, which is inside the box, would move into the opposite direction of your hand movement (because the stick is affixed at the pivot point where it is entering the box through the hole). (I hope you understand what I mean so far.) Now I need to simulate such a setup in a 3d program. I have already successfully developed an Ogre3d framework for this application, including bullet. But what I don't know is how I can implement in my program what I have described above. This application must include two more features: The scene camera is attached to the end of the stick that is inserted into the box. So when the user would move the mouse (to control "his" end of the stick outside the box), then the camera attached to the stick would move in the opposite direction, as described above. The stick has some length, and the user can push it further into the box, or pull it closer to him again. That means of course that the max. radius on which the end of the stick inside the box can move depends on how far the stick is pushed into the box. Thus, the more the stick is pushed into the box, the larger the max. radius of this end of the stick with the camera will be. I understand this is maybe quite a complex thing, so I don't expect any real source code here. I already have the Ogre and bullet part as said up and running, as well as a camera attached to the stick. This works fine. What I don't know though is how I can simulate the setup described above. Especially the requirement that the stick is affixed at the position of the hole on the box, where it is inserted into the box. Any ideas how I could approach to implement the described setup?

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