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Re: generating sparse matricies

From: David Bateman
Subject: Re: generating sparse matricies
Date: Sat, 01 Oct 2005 14:59:08 +0200
User-agent: Mozilla Thunderbird 1.0.2 (Windows/20050317)

Søren Hauberg a écrit :

I can't remember if this works in 2.164, but in 2.9.3 you can just use


fre, 30 09 2005 kl. 23:07 -0700, skrev Paul Roberts:

I am using Octave 2.1.64. I would like to iteratively build a sparse
matrix uring code like:

X = sparse(10000,1000);
for j=1:1000
X(:, j) = rand(10000,1) < 0.01;
Furthermore, if you use a structure like the above in octave 2.9.x (or even matlab for the above case, use spalloc in matlab for the above), you'll reallocate the memory for the sparse matrix at each iteration of the for-loop. Therefore, this is likely to be slow.. Its much better to create three vectors for the row, column and value and create the matrix directly. See section 22.1.2 of the manual in 2.9.3 version of octave. I've written some patchy documentation for the sparse stuff that is in section 22.

Note the assign function isn't implemented in the octave-forge sparse toolbox which is what made me start implementing a new sparse implementation in the first place. So the above won't work, though sprand will.


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