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• Creating dynamic plots

  - by geoff92

  I'm completely new to web programming but I do have a programming background. I'd like to create a site that allows users to visit, enter some specifications into a form, submit the form, and then receive a graph. I have a few questions about this, only because I'm pretty ignorant: Is there a good framework I should start in? I know a lot of java, I'm okay with python, and I learned Ruby in the past. I figure I might use ruby on rails only because I hear of it so often and I think I've also heard it's easy. If anyone has some other recommendation, please suggest. The user will be entering data into a form. I'm guessing the request they'll be making should be one of a GET request, right? Because I don't intend for any of the data they're entering to modify my server (in fact, I don't intend on having a database). The data the user inputs will be used to perform calculations involving lots of matrices. I've written this functionality in python. If I use ruby on rails, should it be instead written in Ruby? Somewhere I've heard that you can either place the load of the work on your server or on the client's computer. Since the code performs heavy math, which option is preferable? How do I alter the setup to either make the client do the work or my server? Should I be using a "cgi-bin"? In the code that I have now, I use matplotlib, a python library, and then "show" the plot in order to see the graph. I specify the x and y limits, but I am able to "drag" the graph in order to see more data within the plot window. Ultimately, I want a graph to be shown on my site with the drag functionality. Is this possible? What if the client drags the graph so far, more computations must be made? Thanks!

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• Calculate Matrix Rank using scipy

  - by Hooked

  I'd like to calculate the mathematical rank of a matrix using scipy. The most obvious function numpy.rank calculates the dimension of an array (ie. scalars have dimension 0, vectors 1, matrices 2, etc...). I am aware that the numpy.linalg.lstsq module has this capability, but I was wondering if such a fundamental operation is built into the matrix class somewhere. Here is an explicit example: from numpy import matrix, rank A = matrix([[1,3,7],[2,8,3],[7,8,1]]) print rank(A) This gives 2 the dimension, where I'm looking for an answer of 3.

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• How do I apply multiple rotation transforms on a Raphael text object?

  - by Pridkett

  I have a Raphael text object that I would like to rotate around an axis some distance away and also rotate the text accordingly so it stays horizontal. I know this is possible using SVG transformation matrices, but the author of Raphael has stated that they won't be a part of the toolkit anytime soon. Here's some code of what I'd like to do: txt_obj = paper.text(100, 0, "Hello!"); txt_obj.rotate(90, 100, 100); // rotate text so it is sideways at (200,100) txt_obj.rotate(-90); // rotate text back to horizontal Unfortunately, the second rotate command obliterates the translation and rotation accomplished by the first. Ideally I'd like to animate the operation, but I'll take it one step at a time for right now.

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• How can I flush the output of disp in Octave?

  - by Nathan Fellman

  I have a program in Octave that has a loop - running a function with various parameters, not something that I can turn into matrices. At the beginning of each iteration I print the current parameters using disp. The first times I ran it I had a brazillion warnings, and then I also got these prints. Now that I cleaned them up, I no longer see them. My guess is that they're stuck in a buffer, and I'll see them when the program ends or the buffer fills. Is there any way to force a flush of the print buffer so that I can see my prints?

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• How do I translate this Matlab bsxfun call to R?

  - by claytontstanley

  I would also (fingers crossed) like the solution to work with R Sparse Matrices in the Matrix package. >> A = [1,2,3,4,5] A = 1 2 3 4 5 >> B = [1;2;3;4;5] B = 1 2 3 4 5 >> bsxfun(@times, A, B) ans = 1 2 3 4 5 2 4 6 8 10 3 6 9 12 15 4 8 12 16 20 5 10 15 20 25 >> EDIT: I would like to do a matrix multiplication of these sparse vectors, and return a sparse array: > class(NRowSums) [1] "dsparseVector" attr(,"package") [1] "Matrix" > class(NColSums) [1] "dsparseVector" attr(,"package") [1] "Matrix" > NRowSums * NColSums (I think) w/o using a non-sparse variable to temporarily store data.

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• Android color picker - updating color array

  - by zorglub76

  Hi all, I'm trying to create a color picker for Android that looks like a minimalistic version of Gimp's. So, it has a hue slider and a rectangle with saturation/value variants of a color chosen in hue slider. Question: what is the best way to create the rectangle? Right now, I'm creating an 200x200 array of pixels, but it takes ~5sec to create and display rectangle with that array. And I need colors in rectangle to change whenever I change the value in hue slider... Rectangle is bitmap, btw. Can I use color matrices on that and how? Any examples? Thanks in advance!

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• In R, when using named rows, can a sparse matrix column be added to another sparse matrix?

  - by ayman

  I have two sparse matrices, m1 and m2: > m1 <- Matrix(data=0,nrow=2, ncol=1, sparse=TRUE, dimnames=list(c("b","d"),NULL)) > m2 <- Matrix(data=0,nrow=2, ncol=1, sparse=TRUE, dimnames=list(c("a","b"),NULL)) > m1["b",1]<- 4 > m2["a",1]<- 5 > m1 2 x 1 sparse Matrix of class "dgCMatrix" b 4 d . > m2 2 x 1 sparse Matrix of class "dgCMatrix" a 5 b . > and I want to cbind() them to make a sparse matrix like: [,1] [,2] a . 5 b 4 . d . . however cbind() ignores the named rows: > cbind(m1[,1],m2[,1]) [,1] [,2] b 4 5 d 0 0 is there some way to do this without a brute force loop?

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• how to build an accumulator array in matlab

  - by schwiz

  I'm very new to matlab so sorry if this is a dumb question. I have to following matrices: im = imread('image.jpg'); %<370x366 double> [y,x] = find(im); %x & y both <1280x1 double> theta; %<370x366 double> computed from gradient of image I can currently plot points one at a time like this: plot(x(502) + 120*cos(theta(y(502),x(502))),y(502) + 120*sin(theta(y(502),x(502))),'*b'); But what I want to do is some how increment an accumulator array, something like this: acc = zeros(size(im)); acc(y,x) = acc(x + 120*cos(theta(y,x)),y + 120*sin(theta(y,x)),'*b')) + 1; It would be nice if the 120 could actually be another matrix containing different radius values as well.

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• loading multiple .mat files in MATLAB

  - by smilingbuddha

  I have 110 files named time1.mat, time2.mat ..., time110.mat. I want to load these matrices into the MATLAB workspace. I have always used load -'ASCII' matrix.mat to load an ASCII matrix file in the current folder. So I tried doing for i=1:10 filename=strcat('time',int2str(i),'.mat'); load -'ASCII' filename end But I am getting a MATLAB error as ??? Error using ==> load Unable to read file filename: No such file or directory. ? Of course the string filename seems to be evaluated correctly by MATLAB as time1.mat. in the first iteration where it crashes at the load line. Any suggestions how I should do this?

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• Computing orientation of a square and displaying an object with the same orientation

  - by Robin

  Hi, I wrote an application which detects a square within an image. To give you a good understanding of how such an image containing such a square, in this case a marker, could look like: What I get, after the detection, are the coordinates of the four corners of my marker. Now I don't know how to display an object on my marker. The object should have the same rotation/angle/direction as the marker. Are there any papers on how to achieve that, any algorithms that I can use that proofed to be pretty solid/working? It doesn't need to be a working solution, it could be a simple description on how to achieve that or something similar. If you point me at a library or something, it should work under linux, windows is not needed but would be great in case I need to port the application at some point. I already looked at the ARToolkit but they you camera parameter files and more complex matrices while I only got the four corner points and a single image instead of a whole video / camera stream.

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• How do I create an empty array/matrix in NumPy?

  - by Ben

  I'm sure I must be being very dumb, but I can't figure out how to use an array or matrix in the way that I would normally use a list. I.e., I want to create an empty array (or matrix) and then add one column (or row) to it at a time. At the moment the only way I can find to do this is like: mat = None for col in columns: if mat is None: mat = col else: mat = hstack((mat, col)) Whereas if it were a list, I'd do something like this: list = [] for item in data: list.append(item) Is there a way to use that kind of notation for NumPy arrays or matrices? (Or a better way -- I'm still pretty new to python!)

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• Clustering [assessment] algorithm with distance matrix as an input

  - by Max

  Can anyone suggest some clustering algorithm which can work with distance matrix as an input? Or the algorithm which can assess the "goodness" of the clustering also based on the distance matrix? At this moment I'm using a modification of Kruskal's algorithm (http://en.wikipedia.org/wiki/Kruskal%27s_algorithm) to split data into two clusters. It has a problem though. When the data has no distinct clusters the algorithm will still create two clusters with one cluster containing one element and the other containing all the rest. In this case I would rather have one cluster containing all the elements and another one which is empty. Are there any algorithms which are capable of doing this type of clustering? Are there any algorithms which can estimate how well the clustering was done or even better how many clusters are there in the data? The algorithms should work only with distance(similarity) matrices as an input.

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• MATLAB using MAT2CELL

  - by Ali

  i have the following matrices letter=[A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ... a b c d e f g h ii jj k l m o p q r s t u v w x y z]; number=[one two three four five six seven eight nine zero]; character =[number letter]; Character becomes a matrix of 42 by 1464, but i would like to break it into cells of 42 by 24 using mat2cell. How can i please do it, every time i try i get an error????

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• VC7.1 C1204 internal compiler error

  - by Nathan Ernst

  I'm working on modifying Firaxis' Civilization 4 core game DLL. The host application is built using VC7, hence the constraint (source not provided for the host EXE). I've been working on rewriting a large chunk of the code (focusing on low-hanging performance issues & memory leaks). I recently ran into an internal compiler error when trying to mod the code to use an array class instead of dynamically allocated 2-d arrays, I was going to use matrices from the boost lib (Civ4 is already using boost, so why not?). Basically, the issue comes down to: if I include "boost/numeric/ublas/matrix.hpp", I run into an internal compiler error C1204. MSDN has this to say: MSDN C1204 KB has this to say: KB 883655 So, I'm curious, is it possible to solve this error without a KB/SP being applied and dramatically reducing the complexity of the code? Additionally, as VC7 is no longer "supported", does anyone have a valid (supported) link for a VC7 service pack?

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• Static Typing and Writing a Simple Matrix Library

  - by duckworthd

  Aye it's been done a million times before, but damnit I want to do it again. I'm writing a simple Matrix Library for C++ with the intention of doing it right. I've come across something that's fairly obvious in mathematics, but not so obvious to a strongly typed system -- the fact that a 1x1 matrix is just a number. To avoid this, I started walking down the hairy path of matrices as a composition of vectors, but also stumbled upon the fact that two vectors multiplied together could either be a number or a dyad, depending on the orientation of the two. My question is, what is the right way to deal with this situation in a strongly typed language like C++ or Java?

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• How to fix rotations in a Rubik's Cube?

  - by Eindbaas

  I'm trying to create a Rubik's Cube in Flash & Papervision and i'm really stuck here. I'm up to the point where i can rotate any plane of cubes once, but after that...it's messed up because all local coordinate systems are messy. I dont really know where to go from here, can anybody give any advice on what do do? I'm not looking for 'read about transformation matrices', i know i should (and i am doing that), but i'm not really sure what to look for. My idea is that, after each rotation, i should fix each coordinate system of each cube again, but i have no idea how. Any hints on what i want to achieve (in words), and why, are much appreciated. http://dl.dropbox.com/u/250155/rubik/main.html (you can press the K key once ;) )

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• Matrix Comparison algorithm

  - by SysAdmin

  If you have 2 Matrices of dimensions N*M. what is the best way to get the difference Rect? Example: 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 4 5 4 3 2 3 <---> 2 3 2 3 2 3 2 3 2 3 4 5 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 | | \ / Rect([2,2] , [3,4]) 4 5 4 4 5 2-> A (2 x 3 Matrix) The best I could think of is to scan from Top-Left hit the point where there is difference. Then scan from Bottom Right and hit the point where there is a difference. But In worst case, this is O(N*M). is there a better efficient algorithm?

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• More complex view matrix calculation required to composite 3d models with 2d video

  - by lzcd

  I'm utilising some 2d / 3d tracking data (provided by pfHoe) to help integrate some 3d models into the playback of some 2d video. Things are working.... okay... but there's still some visible 'slipping' of the models against the video background and I suspect this is may be because the XNA CreatePerspective helper method isn't taking into account some of the additional data supplied by pfHoe such as independent horizontal / vertical field of view angles and focal length. Would anyone be able to point me towards some examples of constructing view matrices that include such details?

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• Looking for actively maintained matrix math library for php

  - by Mnebuerquo

  Does anyone know where I might find a PHP matrix math library which is still actively maintained? I need to be able to do the basic matrix operations like reduce, transpose (including non-square matrices), invert, determinant, etc. This question was asked in the past, then closed with no answers. Now I need an answer to the same question. See these links to related questions: http://stackoverflow.com/questions/428473/matrix-artihmetic-in-php http://stackoverflow.com/questions/435074/matrix-arithmetic-in-php-again I was in the process of installing the pear Math_Matrix library when I saw these and realized it wouldn't help me. (Thanks Ben for putting that comment about transpose in your question.) I can code this stuff myself, but I would make me happier to see that there is a library for this somewhere.

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• How can I learn the math necessary for working with computer vision?

  - by Duncan Benoit

  I know that computer vision involves a lot of math, but I need some tips about how programmers gain that knowledge. I've started to use the OpenCV library but I have some major problems in understanding how the math works in the algorithms. In college I have studied some math and we worked with matrices and derivatives, but I didn't pay to much attention to the subject. It seemed to be so difficult and useless from a programmer point of view. I suppose that there has to be some easy way to understand what a second derivative is without calculating an equation. (Derivatives are just an example) Do you have any tips for me about how can i gain such knowledge? A forum, book, link, advice, anything?

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• Efficient calculation of matrix cumulative standard deviation in r

  - by Abiel

  I recently posted this question on the r-help mailing list but got no answers, so I thought I would post it here as well and see if there were any suggestions. I am trying to calculate the cumulative standard deviation of a matrix. I want a function that accepts a matrix and returns a matrix of the same size where output cell (i,j) is set to the standard deviation of input column j between rows 1 and i. NAs should be ignored, unless cell (i,j) of the input matrix itself is NA, in which case cell (i,j) of the output matrix should also be NA. I could not find a built-in function, so I implemented the following code. Unfortunately, this uses a loop that ends up being somewhat slow for large matrices. Is there a faster built-in function or can someone suggest a better approach? cumsd <- function(mat) { retval <- mat*NA for (i in 2:nrow(mat)) retval[i,] <- sd(mat[1:i,], na.rm=T) retval[is.na(mat)] <- NA retval } Thanks.

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• Array subscript is not an integer

  - by Dimitri

  Hello folks, following this previous question Malloc Memory Corruption in C, now i have another problem. I have the same code. Now I am trying to multiply the values contained in the arrays A * vc and store in res. Then A is set to zero and i do a second multiplication with res and vc and i store the values in A. (A and Q are square matrices and mc and vc are N lines two columns matrices or arrays). Here is my code : int jacobi_gpu(double A[], double Q[], double tol, long int dim){ int nrot, p, q, k, tid; double c, s; double *mc, *vc, *res; int i,kc; double vc1, vc2; mc = (double *)malloc(2 * dim * sizeof(double)); vc = (double *)malloc(2 * dim * sizeof(double)); vc = (double *)malloc(dim * dim * sizeof(double)); if( mc == NULL || vc == NULL){ fprintf(stderr, "pb allocation matricre\n"); exit(1); } nrot = 0; for(k = 0; k < dim - 1; k++){ eye(mc, dim); eye(vc, dim); for(tid = 0; tid < floor(dim /2); tid++){ p = (tid + k)%(dim - 1); if(tid != 0) q = (dim - tid + k - 1)%(dim - 1); else q = dim - 1; printf("p = %d | q = %d\n", p, q); if(fabs(A[p + q*dim]) > tol){ nrot++; symschur2(A, dim, p, q, &c, &s); mc[2*tid] = p; vc[2 * tid] = c; mc[2*tid + 1] = q; vc[2*tid + 1] = -s; mc[2*tid + 2*(dim - 2*tid) - 2] = p; vc[2*tid + 2*(dim - 2*tid) - 2 ] = s; mc[2*tid + 2*(dim - 2*tid) - 1] = q; vc[2 * tid + 2*(dim - 2*tid) - 1 ] = c; } } for( i = 0; i< dim; i++){ for(kc=0; kc < dim; kc++){ if( kc < floor(dim/2)) { vc1 = vc[2*kc + i*dim]; vc2 = vc[2*kc + 2*(dim - 2*kc) - 2]; }else { vc1 = vc[2*kc+1 + i*dim]; vc2 = vc[2*kc - 2*(dim - 2*kc) - 1]; } res[kc + i*dim] = A[mc[2*kc] + i*dim]*vc1 + A[mc[2*kc + 1] + i*dim]*vc2; } } zero(A, dim); for( i = 0; i< dim; i++){ for(kc=0; kc < dim; k++){ if( k < floor(dim/2)){ vc1 = vc[2*kc + i*dim]; vc2 = vc[2*kc + 2*(dim - 2*kc) - 2]; }else { vc1 = vc[2*kc+1 + i*dim]; vc2 = vc[2*kc - 2*(dim - 2*kc) - 1]; } A[kc + i*dim] = res[mc[2*kc] + i*dim]*vc1 + res[mc[2*kc + 1] + i*dim]*vc2; } } affiche(mc,dim,2,"Matrice creuse"); affiche(vc,dim,2,"Valeur creuse"); } free(mc); free(vc); free(res); return nrot; } When i try to compile, i have this error : jacobi_gpu.c: In function ‘jacobi_gpu’: jacobi_gpu.c:103: error: array subscript is not an integer jacobi_gpu.c:103: error: array subscript is not an integer jacobi_gpu.c:118: error: array subscript is not an integer jacobi_gpu.c:118: error: array subscript is not an integer make: *** [jacobi_gpu.o] Erreur 1 The corresponding lines are where I store the results in res and A : res[kc + i*dim] = A[mc[2*kc] + i*dim]*vc1 + A[mc[2*kc + 1] + i*dim]*vc2; and A[kc + i*dim] = res[mc[2*kc] + i*dim]*vc1 + res[mc[2*kc + 1] + i*dim]*vc2; Can someone explain me what is this error and how can i correct it? Thanks for your help. ;)

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• Efficiently compute the row sums of a 3d array in R

  - by Gavin Simpson

  Consider the array a: > a <- array(c(1:9, 1:9), c(3,3,2)) > a , , 1 [,1] [,2] [,3] [1,] 1 4 7 [2,] 2 5 8 [3,] 3 6 9 , , 2 [,1] [,2] [,3] [1,] 1 4 7 [2,] 2 5 8 [3,] 3 6 9 How do we efficiently compute the row sums of the matrices indexed by the third dimension, such that the result is: [,1] [,2] [1,] 12 12 [2,] 15 15 [3,] 18 18 ?? The column sums are easy via the 'dims' argument of colSums(): > colSums(a, dims = 1) but I cannot find a way to use rowSums() on the array to achieve the desired result, as it has a different interpretation of 'dims' to that of colSums(). It is simple to compute the desired row sums using: > apply(a, 3, rowSums) [,1] [,2] [1,] 12 12 [2,] 15 15 [3,] 18 18 but that is just hiding the loop. Are there other efficient, truly vectorised, ways of computing the required row sums?

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• Google App Engine Application Error 5

  - by Sam

  I frequently get this Application error. What does this mean ? File "/base/data/home/apps/0xxopdp/10.347467753731922836/matrices.py", line 215, in insert_into_db obj.put() File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/db/__init__.py", line 895, in put return datastore.Put(self._entity, config=config) File "/base/python_runtime/python_lib/versions/1/google/appengine/api/datastore.py", line 404, in Put return _GetConnection().async_put(config, entities, extra_hook).get_result() File "/base/python_runtime/python_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 601, in get_result self.check_success() File "/base/python_runtime/python_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 572, in check_success rpc.check_success() File "/base/python_runtime/python_lib/versions/1/google/appengine/api/apiproxy_stub_map.py", line 502, in check_success self.__rpc.CheckSuccess() File "/base/python_runtime/python_lib/versions/1/google/appengine/api/apiproxy_rpc.py", line 126, in CheckSuccess raise self.exception ApplicationError: ApplicationError: 5 I do make many calls to the datastore. What caused this problem ?

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• Values of Variables Matrix NumPy

  - by Max Mines

  I'm working on a program that determines if lines intersect. I'm using matrices to do this. I understand all the math concepts, but I'm new to Python and NumPy. I want to add my slope variables and yint variables to a new matrix. They are all floats. I can't seem to figure out the correct format for entering them. Here's an example: import numpy as np x = 2 y = 5 w = 9 z = 12 I understand that if I were to just be entering the raw numbers, it would look something like this: matr = np.matrix('2 5; 9 12') My goal, though, is to enter the variable names instead of the ints.

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