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• Lerping to a center point while in motion

  - by Fibericon

  I have an enemy that initially flies in a circular motion, while facing away from the center point. This is how I achieve that: position.Y = (float)(Math.Cos(timeAlive * MathHelper.PiOver4) * radius + origin.Y); position.X = (float)(Math.Sin(timeAlive * MathHelper.PiOver4) * radius + origin.X); if (timeAlive < 5) { angle = (float)Math.Atan((0 - position.X) / (0 - position.Y)); if (0 < position.Y) RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) * Matrix.CreateRotationZ(-1 * angle); else RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) * Matrix.CreateRotationZ(MathHelper.Pi - angle); } That part works just fine. After five seconds of this, I want the enemy to turn inward, facing the center point. However, I've been trying to lerp to that point, since I don't want it to simply jump to the new rotation. Here's my code for trying to do that: else { float newAngle = -1 * (float)Math.Atan((0 - position.X) / (0 - position.Y)); angle = MathHelper.Lerp(angle, newAngle, (float)gameTime.ElapsedGameTime.Milliseconds / 1000); if (0 < position.Y) RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) * Matrix.CreateRotationZ(MathHelper.Pi - angle); else RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) * Matrix.CreateRotationZ(-1 * angle); } That doesn't work so fine. It seems like it's going to at first, but then it just sort of skips around. How can I achieve what I want here?

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• How to rotate a group of objects around a common center?

  - by user1662292

  I've made a model in 3D Studio Max 9. It consists of a variety of cubes, clyinders etc. In XNA I've imported the model okay and it shows correctly. However, when I apply rotation, each component in the model rotates around it's own centre. I want the model to rotate as a single unit. I've linked the components in 3D Max and they rotate as I want in Max. protected override void LoadContent() { spriteBatch = new SpriteBatch(GraphicsDevice); model = Content.Load<Model>("Models/Alien1"); } protected override void Update(GameTime gameTime) { camera.Update(1f, new Vector3(), graphics.GraphicsDevice.Viewport.AspectRatio); rotation += 0.1f; base.Update(gameTime); } protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(Color.CornflowerBlue); Matrix[] transforms = new Matrix[model.Bones.Count]; model.CopyAbsoluteBoneTransformsTo(transforms); Matrix worldMatrix = Matrix.Identity; Matrix rotationYMatrix = Matrix.CreateRotationY(rotation); Matrix translateMatrix = Matrix.CreateTranslation(location); worldMatrix = rotationYMatrix * translateMatrix; foreach (ModelMesh mesh in model.Meshes) { foreach (BasicEffect effect in mesh.Effects) { effect.World = worldMatrix * transforms[mesh.ParentBone.Index]; effect.View = camera.viewMatrix; effect.Projection = camera.projectionMatrix; effect.EnableDefaultLighting(); effect.PreferPerPixelLighting = true; } mesh.Draw(); } base.Draw(gameTime); } More Info: Rotating the object via it's properties works fine so I'm guessing there's something up with the code rather than with the object itself. Translating the object also causes the objects to get moved independently of each other rather than as a single model and each piece becomes spread around the scene. The model is in .X format.

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• Please help me debug this little C program on dynamic two-dimensional array? [migrated]

  - by azhi

  I am a newbie here. I have written a little C program, which is to create a two-dimensional matrix. Here is the code: #include <stdio.h> #include <stdlib.h> int **CreatMatrix(int m,int n){ int **Matrix; int i; Matrix=(int**)malloc(m*sizeof(int*)); for(i=0;i<m;i++){ Matrix[i]=(int*)malloc(n*sizeof(int)); } return Matrix; } int main(){ int m,n; int **A; printf("Please input the size of the Matrix: "); scanf("%d%d",&m,&n); A=CreatMatrix(m,n); printf("Please input the entries of the Matrix, which should be integers!\n"); int i,j; for(i=0;i<m;i++){ for(j=0;j<n;j++){ scanf("%d",&A[i][j]); } } printf("The Matrix that you input is:\n"); for(i=0;i<m;i++){ for(j=0;j<n;j++){ printf("%3d ",A[i][j]); } printf("\n"); } for(i=0;i<m;i++) free(A[i]); free(A); } I have run it, and it works fine. But I am not sure if it is right? Can anyone help me debug it?

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• Using getRotationMatrix and getOrientation in Android 2.1

  - by aaronmar

  I've been having issues with this for far too long. This code should output dx,dy,dz for the accelerometer, and a running total of the dx. It should also output azimuth, pitch, and roll. I've used info from http://bit.ly/codeUsed, but to no avail. This code does not correctly output pitch, azimuth, or roll. It outputs 0.0, -0.0, -0.0 for the last three textviews, respectively. Please restore my sanity by helping me switch (event.sensor.getType()) { case Sensor.TYPE_ACCELEROMETER: accelerometerValues = event.values.clone(); case Sensor.TYPE_MAGNETIC_FIELD: geomagneticMatrix = event.values.clone(); sensorReady = true; break; default: break; } if (geomagneticMatrix != null && accelerometerValues != null && sensorReady) { sensorReady = false; float[] R = new float[16]; float[] I = new float[16]; SensorManager.getRotationMatrix(R, I, accelerometerValues, geomagneticMatrix); float[] actual_orientation = new float[3]; SensorManager.getOrientation(R, actual_orientation); tvXCoordinate.setText(accelerometerValues[0] + ""); tvYCoordinate.setText(accelerometerValues[1] + ""); tvZCoordinate.setText(accelerometerValues[2] + ""); floatXTotal += accelerometerValues[0]; tvXTotal.setText(floatXTotal + ""); tvAzimuth.setText(actual_orientation[0] + ""); tvPitch.setText(actual_orientation[1] + ""); tvRoll.setText(actual_orientation[2] + ""); }

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• Sparse matrices / arrays in Java

  - by DanM

  I'm working on a project, written in Java, which requires that I build a very large 2-D sparse array. Very sparse, if that makes a difference. Anyway: the most crucial aspect for this application is efficency in terms of time (assume loads of memory, though not nearly so unlimited as to allow me to use a standard 2-D array -- the key range is in the billions in both dimensions). Out of the kajillion cells in the array, there will be several hundred thousand cells which contain an object. I need to be able to modify cell contents VERY quickly. Anyway: Does anyone know a particularly good library for this purpose? It would have to be Berkeley, LGPL or similar license (no GPL, as the product can't be entirely open-sourced). Or if there's just a very simple way to make a homebrew sparse array object, that'd be fine too. I'm considering MTJ, but haven't heard any opinions on its quality. Thanks!! -Dan

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• transpose 1D array of leading dimension N

  - by Simon

  how can i transpose an 1d array of leading dimension N, without extra space ? any language is fine

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• Calculations in a table of data

  - by Christian W

  I have a table of data with survey results, and I want to do certain calculations on this data. The datastructure is somewhat like this: ____________________________________________________________________________________ | group |individual | key | key | key | | | |subkey|subkey|subkey|subkey|subkey|subkey|subkey|subkey|subkey| | | |q|q|q |q |q |q|q|q |q|q|q |q |q |q|q|q |q|q|q |q |q |q|q|q | |-------|-----------|-|-|--|--|---|-|-|--|-|-|--|--|---|-|-|--|-|-|--|--|---|-|-|--| | 1 | 0001 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 1 | 0002 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 1 | 0003 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 2 | 0004 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 2 | 0005 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 3 | 0006 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 4 | 0007 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | ------------------------------------------------------------------------------------ Excuse my poor ascii skills... So, every individual belongs to a group, and has answered some questions. These questions are always grouped in keys and subkeys. Is there any simple method to calculate averages, deviations and similar based on the groupings. Something like public float getAverage(int key, int individual); float avg = getAverage(5,7); I think what I'm asking is what would be the best way to structure the data in C# to make it as easy as possible to work with? I have started making classes for every entity, but I got confused somewhere and something stopped working. So before I continue along this path, I was wondering if there are any other, better, ways of doing this? (Every individual can also have describing variables, like agegroup and such, but that's not important for the base functionality.) Our current solution does all calculations inline in the queries when requesting the data from the database. This works, but it's slow and the number of queries equals questions * individuals + keys * individuals, which could be alot if individual queries. Any suggestions?

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• Need help looping through text file in Objective-C and looping through multidimensional array of dat

  - by Fulvio

  I have a question regarding an iPhone game I'm developing. At the moment, below is the code I'm using to currently I loop through my multidimensional array and position bricks accordingly on my scene. Instead of having multiple two dimensional arrays within my code as per the following (gameLevel1). Ideally, I'd like to read from a text file within my project and loop through the values in that instead. Please take into account that I'd like to have more than one level within my game (possibly 20) so my text file would have to have some sort of separator line item to determine what level I want to render. I was then thinking of having some sort of method that I call and that method would take the level number I'm interested in rendering. e.g. Method to call level based on separator? -(void)renderLevel:(NSString) levelNumber; e.g. Text file example? #LEVEL_ONE# 0,0,0,0,0,0,0,0,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,1,1,1,1,1,1,1,0 0,0,0,0,0,0,0,0,0 #LEVEL_TWO# 1,0,0,0,0,0,0,0,1 1,1,1,1,1,1,1,1,1 1,1,1,1,1,1,1,1,1 1,1,1,1,1,1,1,1,1 1,1,1,1,1,1,1,1,1 0,1,1,1,1,1,1,1,0 1,1,1,1,1,1,1,1,1 0,1,1,1,1,1,1,1,0 1,1,1,1,1,1,1,1,1 0,1,1,1,1,1,1,1,0 1,1,1,1,1,1,1,1,1 0,1,1,1,1,1,1,1,0 1,1,1,1,1,1,1,1,1 1,1,1,1,1,1,1,1,1 1,1,1,1,1,1,1,1,1 1,1,1,1,1,1,1,1,1 1,0,0,0,0,0,0,0,1 Code that I'm currently using: int gameLevel[17][9] = { { 0,0,0,0,0,0,0,0,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,1,1,1,1,1,1,1,0 }, { 0,0,0,0,0,0,0,0,0 } }; for (int row=0; row < 17; row++) { for (int col=0; col < 9; col++) { thisBrickValue = gameLevel[row][col]; xOffset = 35 * floor(col); yOffset = 22 * floor(row); switch (thisBrickValue) { case 0: brick = [[CCSprite spriteWithFile:@"block0.png"] autorelease]; break; case 1: brick = [[CCSprite spriteWithFile:@"block1.png"] autorelease]; break; } brick.position = ccp(xOffset, yOffset); [self addChild:brick]; } }

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• Coordinates in distorted grid

  - by Carsten

  I have a grid in a 2D system like the one in the before image where all points A,B,C,D,A',B',C',D' are given (meaning I know the respective x- and y-coordinates). I need to calculate the x- and y-coordinates of A(new), B(new), C(new) and D(new) when the grid is distorted (so that A' is moved to A'(new), B' is moved to B'(new), C' is moved to C'(new) and D' is moved to D'(new)). The distortion happens in a way in which the lines of the grid are each divided into sub-lines of equal length (meaning for example that AB is divided into 5 parts of the equal length |AB|/5 and A(new)B(new) is divided into 5 parts of the equal length |A(new)B(new)|/5). The distortion is done with the DistortImage class of the Sandy 3D Flash engine. (My practical task is to distort an image using this class where the handles are not positioned at the corners of the image like in this demo but somewhere within it).

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• Sparse (Pseudo) Infinite Grid Data Structure for Web Game

  - by Ming

  I'm considering trying to make a game that takes place on an essentially infinite grid. The grid is very sparse. Certain small regions of relatively high density. Relatively few isolated nonempty cells. The amount of the grid in use is too large to implement naively but probably smallish by "big data" standards (I'm not trying to map the Internet or anything like that) This needs to be easy to persist. Here are the operations I may want to perform (reasonably efficiently) on this grid: Ask for some small rectangular region of cells and all their contents (a player's current neighborhood) Set individual cells or blit small regions (the player is making a move) Ask for the rough shape or outline/silhouette of some larger rectangular regions (a world map or region preview) Find some regions with approximately a given density (player spawning location) Approximate shortest path through gaps of at most some small constant empty spaces per hop (it's OK to be a bad approximation often, but not OK to keep heading the wrong direction searching) Approximate convex hull for a region Here's the catch: I want to do this in a web app. That is, I would prefer to use existing data storage (perhaps in the form of a relational database) and relatively little external dependency (preferably avoiding the need for a persistent process). Guys, what advice can you give me on actually implementing this? How would you do this if the web-app restrictions weren't in place? How would you modify that if they were? Thanks a lot, everyone!

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• How do I remove an array dimension where the elements sum to zero?

  - by James

  I am assigning a 3D array, which contains some information for a number of different loadcases. Each row in the array defines a particular loadcase (of which there are 3) and I would like to remove the loadcase (i.e. the row) if ALL the elements of the row (in 3D) are equal to zero. The code I have at the moment is: Array = zeros(3,5) %# Initialise array Numloadcases = 3; Array(:,:,1) = [10 10 10 10 10; 0 0 0 0 0; 0 0 0 0 0;]; %# Expand to a 3D array Array(:,:,2) = [10 10 10 10 10; 0 0 0 0 0; 0 0 0 0 0;]; Array(:,:,3) = [10 10 10 10 10; 0 0 0 0 0; 0 0 20 0 0;]; Array(:,:,4) = [10 10 10 10 10; 0 0 0 0 0; 0 0 20 0 0;]; %# And to remove the second row: for i = 1:Numloadcases if sum(Array(i,:,:)) == 0 Array(i,:,:) = []; end end At the moment, the for loop I have to remove the rows causes an indexing error, as the size of the array changes in the loop. Can anyone see a work around for this?

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• how to implement a sparse_vector class

  - by Neil G

  I am implementing a templated sparse_vector class. It's like a vector, but it only stores elements that are different from their default constructed value. So, sparse_vector would store the index-value pairs for all indices whose value is not T(). I am basing my implementation on existing sparse vectors in numeric libraries-- though mine will handle non-numeric types T as well. I looked at boost::numeric::ublas::coordinate_vector and eigen::SparseVector. Both store: size_t* indices_; // a dynamic array T* values_; // a dynamic array int size_; int capacity_; Why don't they simply use vector<pair<size_t, T>> data_; My main question is what are the pros and cons of both systems, and which is ultimately better? The vector of pairs manages size_ and capacity_ for you, and simplifies the accompanying iterator classes; it also has one memory block instead of two, so it incurs half the reallocations, and might have better locality of reference. The other solution might search more quickly since the cache lines fill up with only index data during a search. There might also be some alignment advantages if T is an 8-byte type? It seems to me that vector of pairs is the better solution, yet both containers chose the other solution. Why?

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• OpenGL, problems with GL_MODELVIEW GL_PROJECTION...

  - by Marcos Roriz

  Guys, I'm trying to finish up my homework but I'm having some problems here on these models on openGL... any Idea why is my draw not happening? One thing that strange is that if I change to gluPerspective it works.. #include <GL/glut.h> #include <stdlib.h> #include <stdio.h> static int shoulder = 0; static int elbow = 0; void init(void) { glClearColor(1.0, 1.0, 1.0, 0.0); } void display(void) { glClear(GL_COLOR_BUFFER_BIT); glPushMatrix(); /* BASE */ glRotatef((GLfloat) shoulder, 0.0, 0.0, 1.0); glTranslatef(1.0, 0.0, 0.0); glPushMatrix(); //glScalef(2.0, 0.4, 1.0); glBegin(GL_QUADS); glColor3f(0, 0, 0); glVertex2f(0.0, 0.0); glVertex2f(0.0, 10.0); glVertex2f(10.0, 10.0); glVertex2f(10.0, 0.0); glEnd(); glPopMatrix(); glPopMatrix(); glutSwapBuffers(); } void reshape(int w, int h) { glViewport(0, 0, (GLsizei) w, (GLsizei) h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho((GLfloat)-w/2, (GLfloat)w/2, (GLfloat)-h/2, (GLfloat)h/2, -1.0, 1.0); // modo de projecao ortogonal glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glTranslatef(0.0, 0.0, -5.0); } void keyboard(unsigned char key, int x, int y) { switch (key) { case 's': shoulder = (shoulder + 5) % 360; glutPostRedisplay(); break; case 'S': shoulder = (shoulder - 5) % 360; glutPostRedisplay(); break; case 'e': elbow = (elbow + 5) % 360; glutPostRedisplay(); break; case 'E': elbow = (elbow - 5) % 360; glutPostRedisplay(); break; case 27: exit(0); break; default: break; } } int main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); glutInitWindowSize(800, 400); glutInitWindowPosition(100, 100); glutCreateWindow(argv[0]); init(); glutDisplayFunc(display); glutReshapeFunc(reshape); glutKeyboardFunc(keyboard); glutMainLoop(); return 0; }

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• Grid overlayed on image using javascript, need help getting grid coordinates.

  - by Alos

  Hi I am fairly new to javascript and could use some help, I am trying to overlay a grid on top of an image and then be able to have the user click on the grid and get the grid coordinate from the box that the user clicked. I have been working with the code from the following stackoverflow question: Creating a grid overlay over image. link text Here is the code that I have so far: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> </script> <script type="text/javascript"> var SetGrid = function(el, sz, nr, nc){ //get number of rows/columns according to the 'grid' size //numcols = el.getSize().x/sz; //numrows = el.getSize().y/sz; numcols = 48; numrows = 32; //create table element for injecting cols/rows var gridTable = new Element('table', { 'id' : 'gridTable', 'styles' : { 'width' : el.getSize().x, 'height' : el.getSize().y, 'top' : el.getCoordinates().top, 'left' : el.getCoordinates().left } }); //inject rows/cols into gridTable for (row = 1; row<=numrows; row++){ thisRow = new Element('tr', { 'id' : row, 'class' : 'gridRow' }); for(col = 1; col<=numcols; col++){ thisCol = new Element('td', { 'id' : col, 'class' : 'gridCol0' }); //each cell gets down/up over event... down starts dragging|up stops|over draws area if down was fired thisCol.addEvents({ 'mousedown' : function(){ dragFlag = true; startRow = this.getParent().get('id'); startCol = this.get('id'); }, 'mouseup' : function(){ dragFlag = false; }, 'mouseover' : function(){ if (dragFlag==true){ this.set('class', 'gridCol'+$$('#lvlSelect .on').get('value')); } }, 'click' : function(){ //this.set('class', 'gridCol'+$$('#lvlSelect .on').get('id').substr(3, 1) ); str = $$('#lvlSelect .on').get('id'); alert(str.substr(2, 3)); } }); thisCol.inject(thisRow, 'bottom'); }; thisRow.inject(gridTable, 'bottom'); }; gridTable.inject(el.getParent()); } //sens level selector func var SetSensitivitySelector = function(el, sz, nr, nc){ $$('#lvlSelect ul li').each(function(el){ el.addEvents({ 'click' : function(){ $$('#lvlSelect ul li').set('class', ''); this.set('class', 'on'); }, 'mouseover' : function(){ el.setStyle('cursor','pointer'); }, 'mouseout' : function(){ el.setStyle('cursor',''); } }); }); } //execute window.addEvent('load', function(){ SetGrid($('imagetomap'), 32); SetSensitivitySelector(); }); var gridSize = { x: 48, y: 32 }; var img = document.getElementById('imagetomap'); img.onclick = function(e) { if (!e) e = window.event; alert(Math.floor(e.offsetX/ gridSize.x) + ', ' + Math.floor(e.offsetY / gridSize.y)); } </script> <style> #imagetomapdiv { float:left; display: block; } #gridTable { border:1px solid red; border-collapse:collapse; position:absolute; z-index:5; } #gridTable td { opacity:0.2; filter:alpha(opacity=20); } #gridTable .gridCol0 { border:1px solid gray; background-color: none; } #gridTable .gridCol1 { border:1px solid gray; background-color: green; } #gridTable .gridCol2 { border:1px solid gray; background-color: blue; } #gridTable .gridCol3 { border:1px solid gray; background-color: yellow; } #gridTable .gridCol4 { border:1px solid gray; background-color: orange; } #gridTable .gridCol5 { border:1px solid gray; background-color: red; } #lvlSelect ul {float: left; display:block; position:relative; margin-left: 20px; padding: 10px; } #lvlSelect ul li { width:40px; text-align:center; display:block; border:1px solid black; position:relative; padding: 10px; list-style:none; opacity:0.2; filter:alpha(opacity=20); } #lvlSelect ul li.on { opacity:1; filter:alpha(opacity=100); } #lvlSelect ul #li0 { background-color: none; } #lvlSelect ul #li1 { background-color: green; } #lvlSelect ul #li2 { background-color: blue; } #lvlSelect ul #li3 { background-color: yellow; } #lvlSelect ul #li4 { background-color: orange; } #lvlSelect ul #li5 { background-color: red; } </style> </div> <div id="lvlSelect"> <ul> <li value="0" id="li0">0</li> <li value="1" id="li1">1</li> <li value="2" id="li2">2</li> <li value="3" id="li3">3</li> <li value="4" id="li4">4</li> <li value="5" id="li5" class="on">5</li> </ul> </div> In this example the grid box changes color when the image is grid box is clicked, but I would like to be able to have the coordinates of the box. Any help would be great. Thank you

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• What is SVD(singular value decomposition)

  - by shiva

  How does it actually reduce noise..can you suggest some nice tutorials?

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• Is there a substitute for blockproc in Matlab?

  - by SetchSen

  I've been using blockproc for processing images blockwise. Unfortunately, blockproc is part of the Image Processing Toolbox, which I don't have on my personal computer. Is there a combination of functions in base Matlab that can substitute for blockproc? My initial guess was to use im2col to transform each block into columns, and then arrayfun to process each column. Then I realized that im2col is also a part of the Image Processing Toolbox, so that doesn't solve my problem.

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• Is there a name for this type of algorithm?

  - by rehanift

  I have a 2 dimensional array forming a table: [color][number][shape ] ------------------------- [black][10 ][square ] [black][10 ][circle ] [red ][05 ][triangle] [red ][04 ][triangle] [green][11 ][oval ] and what I want to do is group largest common denominators, such that we get: 3 groups group #1: color=black, number=10, shapes = [square, circle] group #2: color=red, shape=triange, numbers = [05,04] group #3: color=green, number=11, shape = oval I wrote code that will handle a 2 "column" scenario, then I needed to adjusted it for 3 and I was figuring I might as well do it for n. I wanted to check first if there is some literature around this but I can't think of what to start looking for!

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• How to interpolate rotations?

  - by uhuu

  I have two vectors describing rotations; a start rotation A and a target rotation B. How would I best go about interpolating A by a factor F to approach B? Using a simple lerp on the vectors fails to work when more than one dimension needs to be interpolated (i.e. produces undesirable rotations). Maybe building quaternions from the rotation vectors and using slerp is the way to go. But how, then, could I extract a vector describing the new rotation from the resulting quaternion? Thanks in advance.

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• Is it possible to shuffle a 2D matrix while preserving row AND column frequencies?

  - by j_random_hacker

  Suppose I have a 2D array like the following: GACTG AGATA TCCGA Each array element is taken from a small finite set (in my case, DNA nucleotides -- {A, C, G, T}). I would like to randomly shuffle this array somehow while preserving both row and column nucleotide frequencies. Is this possible? Can it be done efficiently? [EDIT]: By this I mean I want to produce a new matrix where each row has the same number of As, Cs, Gs and Ts as the corresponding row of the original matrix, and where each column has the same number of As, Cs, Gs and Ts as the corresponding column of the original matrix. Permuting the rows or columns of the original matrix will not achieve this in general. (E.g. for the example above, the top row has 2 Gs, and 1 each of A, C and T; if this row was swapped with row 2, the top row in the resulting matrix would have 3 As, 1 G and 1 T.) It's simple enough to preserve just column frequencies by shuffling a column at a time, and likewise for rows. But doing this will in general alter the frequencies of the other kind. My thoughts so far: If it's possible to pick 2 rows and 2 columns so that the 4 elements at the corners of this rectangle have the pattern XY YX for some pair of distinct elements X and Y, then replacing these 4 elements with YX XY will maintain both row and column frequencies. In the example at the top, this can be done for (at least) rows 1 and 2 and columns 2 and 5 (whose corners give the 2x2 matrix AG;GA), and for rows 1 and 3 and columns 1 and 4 (whose corners give GT;TG). Clearly this could be repeated a number of times to produce some level of randomisation. Generalising a bit, any "subrectangle" induced by a subset of rows and a subset of columns, in which the frequencies of all rows are the same and the frequencies of all columns are the same, can have both its rows and columns permuted to produce a valid complete rectangle. (Of these, only those subrectangles in which at least 1 element is changed are actually interesting.) Big questions: Are all valid complete matrices reachable by a series of such "subrectangle rearrangements"? I suspect the answer is yes. Are all valid subrectangle rearrangements decomposable into a series of 2x2 swaps? I suspect the answer is no, but I hope it's yes, since that would seem to make it easier to come up with an efficient algorithm. Can some or all of the valid rearrangements be computed efficiently? This question addresses a special case in which the set of possible elements is {0, 1}. The solutions people have come up with there are similar to what I have come up with myself, and are probably usable, but not ideal as they require an arbitrary amount of backtracking to work correctly. Also I'm concerned that only 2x2 swaps are considered. Finally, I would ideally like a solution that can be proven to select a matrix uniformly at random from the set of all matrices having identical row frequencies and column frequencies to the original. I know, I'm asking for a lot :)

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• Two dimensional strings in C++

  - by dada

  I want to write something like 2d strings in C++. I tried with : vector< vector<string> > table; int m,n,i,j; string s; cin>>n>>m; for(i=0;i<n;i++) { for(j=0;j<m;j++) { cin>>s; table[i][j] = s; } } cout << "\n\n\n\n"; for(i=0;i<n;i++) { for(j=0;j<m;j++) { cout<<table[i][j]<<" "; } cout<<"\n"; } no compile errors, but when i enter input like: 10 20 .....#.............. .....#.............. .....#.............. .....#.............. ######.............. .......###.......... .......#.#.......... .......###...####### .............#.....# .............####### It gives me segmentation fault. Why ? What's wrong ? And how it should be done so it would work correctly ? Thank you.

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• How can I use from ismember

  - by ahmad hosseini

  Assuming A=[32512199.30 5401000.29 347.33 32512199.69 5401000.45 347.39 32512199.67 5401001.32 353.58 32512199.96 5401001.50 346.99 32512196.71 5401001.69 346.62 ] and B=[32512199.30 5401000.29 347.33 32512199.69 5401000.45 347.39 32512199.67 5401001.32 347.00 32512198.85 5401000.91 347.25 32512196.71 5401001.69 346.87 ] I want using ismember extract the rows that have same X and Y and different Z. X is first column, Y is the second and Z is third. in A and B I want extract from A 32512199.67 5401001.32 353.58 and 32512196.71 5401001.69 346.62 OR from B 32512199.67 5401001.32 347.00 and 32512196.71 5401001.69 346.87 How can I do it?

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• Help with calculation to steer ship in 3d space

  - by Aaron Anodide

  I'm a beginner using XNA to try and make a 3D Asteroids game. I'm really close to having my space ship drive around as if it had thrusters for pitch and yaw. The problem is I can't quite figure out how to translate the rotations, for instance, when I pitch forward 45 degrees and then start to turn - in this case there should be rotation being applied to all three directions to get the "diagonal yaw" - right? I thought I had it right with the calculations below, but they cause a partly pitched forward ship to wobble instead of turn.... :( Here's current (almost working) calculations for the Rotation acceleration: float accel = .75f; // Thrust +Y / Forward if (currentKeyboardState.IsKeyDown(Keys.I)) { this.ship.AccelerationY += (float)Math.Cos(this.ship.RotationZ) * accel; this.ship.AccelerationX += (float)Math.Sin(this.ship.RotationZ) * -accel; this.ship.AccelerationZ += (float)Math.Sin(this.ship.RotationX) * accel; } // Rotation +Z / Yaw if (currentKeyboardState.IsKeyDown(Keys.J)) { this.ship.RotationAccelerationZ += (float)Math.Cos(this.ship.RotationX) * accel; this.ship.RotationAccelerationY += (float)Math.Sin(this.ship.RotationX) * accel; this.ship.RotationAccelerationX += (float)Math.Sin(this.ship.RotationY) * accel; } // Rotation -Z / Yaw if (currentKeyboardState.IsKeyDown(Keys.K)) { this.ship.RotationAccelerationZ += (float)Math.Cos(this.ship.RotationX) * -accel; this.ship.RotationAccelerationY += (float)Math.Sin(this.ship.RotationX) * -accel; this.ship.RotationAccelerationX += (float)Math.Sin(this.ship.RotationY) * -accel; } // Rotation +X / Pitch if (currentKeyboardState.IsKeyDown(Keys.F)) { this.ship.RotationAccelerationX += accel; } // Rotation -X / Pitch if (currentKeyboardState.IsKeyDown(Keys.D)) { this.ship.RotationAccelerationX -= accel; } I'm combining that with drawing code that does a rotation to the model: public void Draw(Matrix world, Matrix view, Matrix projection, TimeSpan elsapsedTime) { float seconds = (float)elsapsedTime.TotalSeconds; // update velocity based on acceleration this.VelocityX += this.AccelerationX * seconds; this.VelocityY += this.AccelerationY * seconds; this.VelocityZ += this.AccelerationZ * seconds; // update position based on velocity this.PositionX += this.VelocityX * seconds; this.PositionY += this.VelocityY * seconds; this.PositionZ += this.VelocityZ * seconds; // update rotational velocity based on rotational acceleration this.RotationVelocityX += this.RotationAccelerationX * seconds; this.RotationVelocityY += this.RotationAccelerationY * seconds; this.RotationVelocityZ += this.RotationAccelerationZ * seconds; // update rotation based on rotational velocity this.RotationX += this.RotationVelocityX * seconds; this.RotationY += this.RotationVelocityY * seconds; this.RotationZ += this.RotationVelocityZ * seconds; Matrix translation = Matrix.CreateTranslation(PositionX, PositionY, PositionZ); Matrix rotation = Matrix.CreateRotationX(RotationX) * Matrix.CreateRotationY(RotationY) * Matrix.CreateRotationZ(RotationZ); model.Root.Transform = rotation * translation * world; model.CopyAbsoluteBoneTransformsTo(boneTransforms); foreach (ModelMesh mesh in model.Meshes) { foreach (BasicEffect effect in mesh.Effects) { effect.World = boneTransforms[mesh.ParentBone.Index]; effect.View = view; effect.Projection = projection; effect.EnableDefaultLighting(); } mesh.Draw(); } }

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• Servlet stops without giving any exception

  - by Fahim

  Hi, I have implemented a Servlet hosted on Tomcat 6 server on Mandriva Linux. I have been able to make the client communicate with the Servlet. In response to a request the Servlet tries to instantiate a another class (named KalmanFilter) located in the same directory. The KalmanFilter tries to create four Matrices (using Jama Matrix package). But at this point Servlet stops without giving any exception ! However, from another test code in the same directory I have been able to create instance of KalmanFilter class, and proceed without any error. The problem occurs only when my Servlet tries to instantiate the KalmanFilter class and create the matrices. Any idea? Below are the codes: MyServlet.java import javax.servlet.*; import javax.servlet.http.*; import java.io.*; import java.util.*; public class MyServlet extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{ doGet(request, response); } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException{ PrintWriter out = null; //response.getWriter(); try{ System.out.println("creating new KalmanFilter"); KalmanFilter filter = new KalmanFilter(); out = response.getWriter(); out.print("filter created"); }catch(Exception ex){ ex.printStackTrace(); System.out.println("Exception in doGet(): " + ex.getMessage()); ex.printStackTrace(out); } } } KalmanFilter.java import Jama.Matrix; public class KalmanFilter { protected Matrix X, X0; protected Matrix F, Q; //protected Matrix F, B, U, Q; protected Matrix H, R; protected Matrix P, P0; private final double EPSILON = 0.001; public KalmanFilter(){ System.out.println("from constructor of KalmanFilter"); createInitialMatrices(); } private void createInitialMatrices(){ System.out.println("from KalmanFilter.createInitialMatrices()"); double[][] pVals = { {1.0, 0.0}, {0.0, 1.0} }; double[][] qVals = { {EPSILON, EPSILON}, {EPSILON, EPSILON} }; double[][] hVals = { {1.0, 0.0}, {0.0, 1.0}, {1.0, 0.0}, {0.0, 1.0} }; double[][] xVals = { {0.0}, {0.0}, }; System.out.println("creating P Q H X matrices in createInitialMatrices()"); try{ this.P = new Matrix(pVals); System.out.println("created P matrix in createInitialMatrices()"); this.Q = new Matrix(qVals); System.out.println("created Q matrix in createInitialMatrices()"); this.H = new Matrix(hVals); System.out.println("created H matrix in createInitialMatrices()"); this.X = new Matrix(xVals); System.out.println("created X matrix in createInitialMatrices()"); System.out.println("created P Q H X matrices in createInitialMatrices()"); }catch(Exception e){ System.out.println("Exception from createInitialMatrices()"+ e.getMessage()); e.printStackTrace(); } System.out.println("returning from createInitialMatrices()"); } }

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• Incremental PCA

  - by smichak

  Hi, Lately, I've been looking into an implementation of an incremental PCA algorithm in python - I couldn't find something that would meet my needs so I did some reading and implemented an algorithm I found in some paper. Here is the module's code - the relevant paper on which it is based is mentioned in the module's documentation. I would appreciate any feedback from people who are interested in this. Micha #!/usr/bin/env python """ Incremental PCA calculation module. Based on P.Hall, D. Marshall and R. Martin "Incremental Eigenalysis for Classification" which appeared in British Machine Vision Conference, volume 1, pages 286-295, September 1998. Principal components are updated sequentially as new observations are introduced. Each new observation (x) is projected on the eigenspace spanned by the current principal components (U) and the residual vector (r = x - U(U.T*x)) is used as a new principal component (U' = [U r]). The new principal components are then rotated by a rotation matrix (R) whose columns are the eigenvectors of the transformed covariance matrix (D=U'.T*C*U) to yield p + 1 principal components. From those, only the first p are selected. """ __author__ = "Micha Kalfon" import numpy as np _ZERO_THRESHOLD = 1e-9 # Everything below this is zero class IPCA(object): """Incremental PCA calculation object. General Parameters: m - Number of variables per observation n - Number of observations p - Dimension to which the data should be reduced """ def __init__(self, m, p): """Creates an incremental PCA object for m-dimensional observations in order to reduce them to a p-dimensional subspace. @param m: Number of variables per observation. @param p: Number of principle components. @return: An IPCA object. """ self._m = float(m) self._n = 0.0 self._p = float(p) self._mean = np.matrix(np.zeros((m , 1), dtype=np.float64)) self._covariance = np.matrix(np.zeros((m, m), dtype=np.float64)) self._eigenvectors = np.matrix(np.zeros((m, p), dtype=np.float64)) self._eigenvalues = np.matrix(np.zeros((1, p), dtype=np.float64)) def update(self, x): """Updates with a new observation vector x. @param x: Next observation as a column vector (m x 1). """ m = self._m n = self._n p = self._p mean = self._mean C = self._covariance U = self._eigenvectors E = self._eigenvalues if type(x) is not np.matrix or x.shape != (m, 1): raise TypeError('Input is not a matrix (%d, 1)' % int(m)) # Update covariance matrix and mean vector and centralize input around # new mean oldmean = mean mean = (n*mean + x) / (n + 1.0) C = (n*C + x*x.T + n*oldmean*oldmean.T - (n+1)*mean*mean.T) / (n + 1.0) x -= mean # Project new input on current p-dimensional subspace and calculate # the normalized residual vector g = U.T*x r = x - (U*g) r = (r / np.linalg.norm(r)) if not _is_zero(r) else np.zeros_like(r) # Extend the transformation matrix with the residual vector and find # the rotation matrix by solving the eigenproblem DR=RE U = np.concatenate((U, r), 1) D = U.T*C*U (E, R) = np.linalg.eigh(D) # Sort eigenvalues and eigenvectors from largest to smallest to get the # rotation matrix R sorter = list(reversed(E.argsort(0))) E = E[sorter] R = R[:,sorter] # Apply the rotation matrix U = U*R # Select only p largest eigenvectors and values and update state self._n += 1.0 self._mean = mean self._covariance = C self._eigenvectors = U[:, 0:p] self._eigenvalues = E[0:p] @property def components(self): """Returns a matrix with the current principal components as columns. """ return self._eigenvectors @property def variances(self): """Returns a list with the appropriate variance along each principal component. """ return self._eigenvalues def _is_zero(x): """Return a boolean indicating whether the given vector is a zero vector up to a threshold. """ return np.fabs(x).min() < _ZERO_THRESHOLD if __name__ == '__main__': import sys def pca_svd(X): X = X - X.mean(0).repeat(X.shape[0], 0) [_, _, V] = np.linalg.svd(X) return V N = 1000 obs = np.matrix([np.random.normal(size=10) for _ in xrange(N)]) V = pca_svd(obs) print V[0:2] pca = IPCA(obs.shape[1], 2) for i in xrange(obs.shape[0]): x = obs[i,:].transpose() pca.update(x) U = pca.components print U

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• Quaternion Camera Orbiting around a Sphere

  - by jessejuicer

  Background: I'm trying to create a game where the camera is always rotating around a single sphere. I'm using the DirectX D3DX math functions in C++ on Windows. The Problem: I cannot get both the camera position and orientation both working properly at the same time. Either one works but not both together. Here's the code for my quaternion camera that revolves around a sphere, always looking at the centerpoint of the sphere, ... as far as I understand it (but which isn't working properly): (I'm only going to present rotation around the X axis here, to simplify this post) Whenever the UP key is pressed or held down, the camera should rotate around the X axis, while looking at the centerpoint of the sphere (which is at 0,0,0 in the world). So, I build a quaternion that represents a small angle of rotation around the x axis like this (where 'deltaAngle' is a small enough number for a slow rotation): D3DXVECTOR3 rotAxis; D3DXQUATERNION tempQuat; tempQuat.x = 0.0f; tempQuat.y = 0.0f; tempQuat.z = 0.0f; tempQuat.w = 1.0f; rotAxis.x = 1.0f; rotAxis.y = 0.0f; rotAxis.z = 0.0f; D3DXQuaternionRotationAxis(&tempQuat, &rotAxis, deltaAngle); ...and I accumulate the result into the camera's current orientation quat, like this: D3DXQuaternionMultiply(&cameraOrientationQuat, &cameraOrientationQuat, &tempQuat); ...which all works fine. Now I need to build a view matrix to pass to DirectX SetTransform function. So I build a rotation matrix from the camera orientation quat as follows: D3DXMATRIXA16 rotationMatrix; D3DXMatrixIdentity(&rotationMatrix); D3DXMatrixRotationQuaternion(&rotationMatrix, &cameraOrientationQuat); ...Now (as seen below) if I just transpose that rotationMatrix and plug it into the 3x3 section of the view matrix, then negate the camera's position and plug it into the translation section of the view matrix, the rotation magically works. Perfectly. (even when I add in rotations for all three axes). There's no gimbal lock, just a smooth rotation all around in any direction. BUT- this works even though I never change the camera's position. At all. Which sorta blows my mind. I even display the camera position and can watch it stay constant at it's starting point (0.0, 0.0, -4000.0). It never moves, but the rotation around the sphere is perfect. I don't understand that. For proper view rotation, the camera position should be revolving around the sphere. Here's the rest of building the view matrix (I'll talk about the commented code below). Note that the camera starts out at (0.0, 0.0, -4000.0) and m_camDistToTarget is 4000.0: /* D3DXVECTOR3 vec1; D3DXVECTOR4 vec2; vec1.x = 0.0f; vec1.y = 0.0f; vec1.z = -1.0f; D3DXVec3Transform(&vec2, &vec1, &rotationMatrix); g_cameraActor->pos.x = vec2.x * g_cameraActor->m_camDistToTarget; g_cameraActor->pos.y = vec2.y * g_cameraActor->m_camDistToTarget; g_cameraActor->pos.z = vec2.z * g_cameraActor->m_camDistToTarget; */ D3DXMatrixTranspose(&g_viewMatrix, &rotationMatrix); g_viewMatrix._41 = -g_cameraActor->pos.x; g_viewMatrix._42 = -g_cameraActor->pos.y; g_viewMatrix._43 = -g_cameraActor->pos.z; g_viewMatrix._44 = 1.0f; g_direct3DDevice9->SetTransform( D3DTS_VIEW, &g_viewMatrix ); ...(The world matrix is always an identity, and the perspective projection works fine). ...So, without the commented code being compiled, the rotation works fine. But to be proper, for obvious reasons, the camera position should be rotating around the sphere, which it currently is not. That's what the commented code is supposed to do. And when I add in that chunk of code to do that, and look at all the data as I hold the keys down (using UP, DOWN, LEFT, RIGHT to rotate different directions) all the values look correct! The camera position is rotating around the sphere just fine, and I can watch that happen visually too. The problem is that the camera orientation does not lookat the center of the sphere. It always looks straight forward down the z axis (toward positive z) as it revolves around the sphere. Yet the values of both the rotation matrix and the view matrix seem to be behaving correctly. (The view matrix orientation is the same as the rotation matrix, just transposed). For instance if I just hold down the key to spin around the x axis, I can watch the values of the three axes represented in the view matrix (x, y, and z axes)... view x-axis stays at (1.0, 0.0, 0.0), and view y-axis and z-axis both spin around the x axis just fine. All the numbers are changing as they should be... well, almost. As far as I can tell, the position of the view matrix is spinning around the sphere one direction (like clockwise), and the orientation (the axes in the view matrix) are spinning the opposite direction (like counter-clockwise). Which I guess explains why the orientation appears to stay straight ahead. I know the position is correct. It revolves properly. It's the orientation that's wrong. Can anyone see what am I doing wrong? Am I using these functions incorrectly? Or is my algorithm flawed? As usual I've been combing my code for simple mistakes for many hours. I'm willing to post the actual code, and a video of the behavior, but that will take much more effort. Thought I'd ask this way first.

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