On Wed, Apr 1, 2009 at 4:15 PM, r
<address@hidden> wrote:
I've recently hit a performance problem with a "for" loop producing
vectors of data. Consider the following (deliberately simple) example:
function retval = test(n)
# retval = zeros(1, n);
for n = [1:n]
retval(n) = n;
endfor
endfunction
octave:26> tic;test(10000);toc
Elapsed time is 0.8 seconds.
octave:27> tic;test(100000);toc
Elapsed time is 72 seconds.
So the complexity is O(n^2).
The same function with a preallocated retval vector:
function retval = test2(n)
retval = zeros(1, n);
for n = [1:n]
retval(n) = n;
endfor
endfunction
has a complexity of O(n):
octave:29> tic;test2(10000);toc
Elapsed time is 0.16 seconds.
octave:30> tic;test2(100000);toc
Elapsed time is 1.9 seconds.
Is it possible to adjust the Octave's allocation algorithm so that it
could allocate larger chunks of data (or growing chunks of data)?
Regards,
-r.
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