Help understand the sumsqr algorithm
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For a current project, I've begun switching between versions of matlab. For my trial of 2014, I guess I didn't download the neural network toolbox, so I can't use sumsqr. When I used it on my other version I got what might be called an "impossible" answer.
In the study of wavelet compression techniques, one expects the original picture and the wavelet transform image to have the same energy. Energy is defined as the sum of squared elements of thee matrix. When I computed sumsqr on my MATLAB 2008, I got two different answers.
In order to try and understand the problem, I have 2 requests for the user community 1. Help me understand sumsqr. Does it square entries first, or sum the matrix first? 2 Is there code for qhat I want to do? That is, square the elements first, then sum them.
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Greg Heath
2014-11-21
1 个投票
help sumsqr
doc sumsqr
type sumsqr
Thank you for formally accepting my answer
Greg
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Roger Stafford
2014-11-21
If you consult the site
http://www.mathworks.com/help/nnet/ref/sumsqr.html
you will see that 'sumsqr' returns with the sum of the squares of all finite elements of a matrix (or cell array of matrices,) as well as their number. For a matrix the following code should suffice, though it might not be as efficient as Mathworks' function. To make it work for cell arrays would require some modifications which I leave to you.
function [s,n] = sumsqr(x)
x = x(:);
t = isfinite(x);
s = sum(x(t).^2);
n = sum(t);
return
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