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Search found 1886 results on 76 pages for 'matrix convolution'.

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  • Can FFT length affect filtering accuracy?

    - by Charles
    Hi, I am designing a fractional delay filter, and my lagrange coefficient of order 5 h(n) have 6 taps in time domain. I have tested to convolute the h(n) with x(n) which is 5000 sampled signal using matlab, and the result seems ok. When I tried to use FFT and IFFT method, the output is totally wrong. Actually my FFT is computed with 8192 data in frequency domain, which is the nearest power of 2 for 5000 signal sample. For the IFFT portion, I convert back the 8192 frequency domain data back to 5000 length data in time domain. So, the problem is, why this thing works in convolution, but not in FFT multiplication. Does converting my 6 taps h(n) to 8192 taps in frequency domain causes this problem? Actually I have tried using overlap-save method, which perform the FFT and multiplication with smaller chunks of x(n) and doing it 5 times separately. The result seems slight better than the previous, and at least I can see the waveform pattern, but still slightly distorted. So, any idea where goes wrong, and what is the solution. Thank you.

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  • Parallelize or vectorize all-against-all operation on a large number of matrices?

    - by reve_etrange
    I have approximately 5,000 matrices with the same number of rows and varying numbers of columns (20 x ~200). Each of these matrices must be compared against every other in a dynamic programming algorithm. In this question, I asked how to perform the comparison quickly and was given an excellent answer involving a 2D convolution. Serially, iteratively applying that method, like so list = who('data_matrix_prefix*') H = cell(numel(list),numel(list)); for i=1:numel(list) for j=1:numel(list) if i ~= j eval([ 'H{i,j} = compare(' char(list(i)) ',' char(list(j)) ');']); end end end is fast for small subsets of the data (e.g. for 9 matrices, 9*9 - 9 = 72 calls are made in ~1 s). However, operating on all the data requires almost 25 million calls. I have also tried using deal() to make a cell array composed entirely of the next element in data, so I could use cellfun() in a single loop: # who(), load() and struct2cell() calls place k data matrices in a 1D cell array called data. nextData = cell(k,1); for i=1:k [nextData{:}] = deal(data{i}); H{:,i} = cellfun(@compare,data,nextData,'UniformOutput',false); end Unfortunately, this is not really any faster, because all the time is in compare(). Both of these code examples seem ill-suited for parallelization. I'm having trouble figuring out how to make my variables sliced. compare() is totally vectorized; it uses matrix multiplication and conv2() exclusively (I am under the impression that all of these operations, including the cellfun(), should be multithreaded in MATLAB?). Does anyone see a (explicitly) parallelized solution or better vectorization of the problem?

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  • Filter design for audio signal.

    - by beanyblue
    What I am trying to do is simple. I have a few .wav files. I want to remove noise and filter out specific frequencies. I don't have matlab and I intend to write my own code for all the filters. Right now, I have a way to read the .wav file and dump out the structure into a text file. My questions are the following: Can I directly apply the digital filters on this sampled data?{ ie, can I directly do a convolution between my input samples and h(n) for the filter function that i choose?). How do I choose the number of coefficients for the Window function? I have octave, so if someone can point me to anything that gives me some idea on how to process the .wav file using octave, that would be great too. I want to be able to filter out the frequency and then listen to the sound again. Is this possible with octave? I'm just a beginner with these kinds of things, so please bear with me if my questions are too naive. Any help will be great.

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  • How can I speed-up this loop (in C)?

    - by splicer
    Hi! I'm trying to parallelize a convolution function in C. Here's the original function which convolves two arrays of 64-bit floats: void convolve(const Float64 *in1, UInt32 in1Len, const Float64 *in2, UInt32 in2Len, Float64 *results) { UInt32 i, j; for (i = 0; i < in1Len; i++) { for (j = 0; j < in2Len; j++) { results[i+j] += in1[i] * in2[j]; } } } In order to allow for concurrency (without semaphores), I created a function that computes the result for a particular position in the results array: void convolveHelper(const Float64 *in1, UInt32 in1Len, const Float64 *in2, UInt32 in2Len, Float64 *result, UInt32 outPosition) { UInt32 i, j; for (i = 0; i < in1Len; i++) { if (i > outPosition) break; j = outPosition - i; if (j >= in2Len) continue; *result += in1[i] * in2[j]; } } The problem is, using convolveHelper slows down the code about 3.5 times (when running on a single thread). Any ideas on how I can speed-up convolveHelper, while maintaining thread safety?

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  • iPhone SDK Zoom and refresh PDF with Quartz

    - by Ben
    Looking at the QuartzDemo sample application, I love the speed of the PDF rending using quartz alone (that is, without using uiwebview). However, when I'm zooming in the PDF it doesn't seem to become more clear like it does in PDF view. Is there something that I can change to have the same effect when zooming in and out using multitouch? like manipulate the PDF transformation matrix or something? Thanks a bunch. --Ben

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  • MATLAB: vectorized array creation from a list of start/end indices

    - by merv
    I have a two-column matrix M that contains the start/end indices of a bunch of intervals: startInd EndInd 1 3 6 10 12 12 15 16 How can I generate a vector of all the interval indices: v = [1 2 3 6 7 8 9 10 12 15 16]; I'm doing the above using loops, but I'm wondering if there's a more elegant vectorized solution? v = []; for i=1:size(M,1) v = [v M(i,1):M(i,2)]; end

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  • Need good RDLC examples/samples

    - by Sachin
    I am in evaluation phase of report tool. I prefer RDLC for the same. But I need some examples/samples available in the wild which can guide us on using the RDLC off the shelf. I would be looking for examples from as simple as list of data and as complex as using matrix, calculation, grouping, etc. This will help us to make a reference point if anytime we get stuck up somewhere.

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  • Do any JS implementations currently support (or have support on the roadmap for) fast, vectorized op

    - by agnoster
    I'd like to do a bit of matrix/vector arithmetic in JavaScript, and was wondering if any browsers or other JS implementations actually have support for vectorized operations, for instance for quickly summing the entries of two Arrays (or summing, or whatever). Even if that currently doesn't mean it compiles down to vectorized operations, at least some language support would be nice for when it does get implemented - I'd take the existence of functions or syntax to support it as a step in the right direction. (Understandably, "vectorization javascript" searches are pretty much all about graphics and SVG.)

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  • Compatibility between JBoss Cache to JBoss Server

    - by Spiderman
    Our application runs succesfully on Tomcat, Websphere and Weblogic and as part of it uses Jboss Cache version 3.1.0.G. Now we would like adjust our app to run also in Jboss server environment. Is there any Jboss server version that can co-exist working together with JBoss cache of this version (3.1)? I couldn't find a match in a compatibility matrix that Jboss publish here: http://www.jboss.org/jbosscache/compatibility.html Related issue (http://stackoverflow.com/questions/2849036/configure-jboss-cache-to-run-on-jboss-server-4-2-3-ga)

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  • Creating a Colormap Legend in Matplotlib

    - by Vince
    Hi fellow Stackers! I am using imshow() in matplotlib like so: import numpy as np import matplotlib.pyplot as plt mat = '''SOME MATRIX''' plt.imshow(mat, origin="lower", cmap='gray', interpolation='nearest') plt.show() How do I add a legend showing the numeric value for the different shades of gray. Sadly, my googling has not uncovered an answer :( Thank you in advance for the help. Vince

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  • selecting the pixels from an image in opencv

    - by ajith
    hi everyone, this is refined version of my previous question http://stackoverflow.com/questions/2602628/computing-matting-laplacian-matrix-of-an-image actually i want to do following operation... summation for all k|(i,j)?wk [(Ii-µk)*(Ij-µk)]...where wk is 3X3 window & µk is mean of wk...here i dont know how to select Ii & Ij separately from an image which is 2 dimensional[Iij]...or does the eqn means anything else??please someone help me..

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  • Is there a Pair-Wise PostHoc Comparisons for the Chi-Square Test in R?

    - by Tal Galili
    Hi all, I am wondering if there exists in R a package/function to perform the: "Post Hoc Pair-Wise Comparisons for the Chi-Square Test of Homogeneity of Proportions" (or an equivalent of it) Which is described here: http://epm.sagepub.com/cgi/content/abstract/53/4/951 My situation is of just making a chi test, on a 2 by X matrix. I found a difference, but I want to know which of the columns is "responsible" for the difference. Thanks, Tal

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  • Python: unable to inherit from a C extension.

    - by celil
    I am trying to add a few extra methods to a matrix type from the pysparse library. Apart from that I want the new class to behave exactly like the original, so I chose to implement the changes using inheritance. However, when I try from pysparse import spmatrix class ll_mat(spmatrix.ll_mat): pass this results in the following error TypeError: Error when calling the metaclass bases cannot create 'builtin_function_or_method' instances What is this causing this error? Is there a way to use delegation so that my new class behaves exactly the same way as the original?

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  • wrapping boost::ublas with swig

    - by leon
    I am trying to pass data around the numpy and boost::ublas layers. I have written an ultra thin wrapper because swig cannot parse ublas' header correctly. The code is shown below #include <boost/numeric/ublas/vector.hpp> #include <boost/numeric/ublas/matrix.hpp> #include <boost/lexical_cast.hpp> #include <algorithm> #include <sstream> #include <string> using std::copy; using namespace boost; typedef boost::numeric::ublas::matrix<double> dm; typedef boost::numeric::ublas::vector<double> dv; class dvector : public dv{ public: dvector(const int rhs):dv(rhs){;}; dvector(); dvector(const int size, double* ptr):dv(size){ copy(ptr, ptr+sizeof(double)*size, &(dv::data()[0])); } ~dvector(){} }; with the SWIG interface that looks something like %apply(int DIM1, double* INPLACE_ARRAY1) {(const int size, double* ptr)} class dvector{ public: dvector(const int rhs); dvector(); dvector(const int size, double* ptr); %newobject toString; char* toString(); ~dvector(); }; I have compiled them successfully via gcc 4.3 and vc++9.0. However when I simply run a = dvector(array([1.,2.,3.])) it gives me a segfault. This is the first time I use swigh with numpy and not have fully understanding between the data conversion and memory buffer passing. Does anyone see something obvious I have missed? I have tried to trace through with a debugger but it crashed within the assmeblys of python.exe. I have no clue if this is a swig problem or of my simple wrapper. Anything is appreciated.

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  • Sliding window algorithm for activiting recognition MATLAB

    - by csc
    I want to write a sliding window algorithm for use in activity recognition. The training data is <1xN so I'm thinking I just need to take (say window_size=3) the window_size of data and train that. I also later want to use this algorithm on a matrix . I'm new to matlab so i need any advice/directions on how to implement this correctly.

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  • boost ublas: rotate 2d vector

    - by AndreasT
    Erm. I hope I am seriously overlooking something. I want to rotate a 2d vector (kartesian) v by a certain angle phi. I can't find a function that generates the appropriate matrix or just performs that function. I know how to do this by hand. I am looking for a ublas utility "something" that does this for me.

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  • matlab write image into eps file

    - by Tim
    In MATLAB, how do you write a matrix into an image of eps format? It seems imwrite does not support eps? convert is not working on the Linux server I am using $ convert exploss_stumps.jpg exploss_stumps.eps convert: missing an image filename `exploss_stumps.eps' @ convert.c/ConvertImageCommand/2838 Any idea why?

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  • matplotlib analog of R's `pairs`

    - by bgbg
    R has a useful function pairs that provides nice matrix of plots of pairwise connections between variables in a data set. The resulting plot looks similar to the following figure, copied from this blog post: Is there any ready to use function based on python's matplolib? I have searched its gallery, but couldn't find anything that resembles what I need. Technically, this should be a simple task, but proper handling of all the possible cases, labels, titles, etc is very tedious.

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  • Can't compare the norm of a vector to 1 in matlab

    - by Ian
    I'm trying to find out wether a matrix is orthonormal. I begin by checking if the vectors are normal by doing for j=1:2; if norm(S:,j) ~= 1; return; % Not normal vector end end But when norm returns 1.0000 comparing that to 1 is true and the function returns, which is not what i want. Any ideas? Thx

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