Re: help with vectorizing a for loop

[Rick T]

Using this code

inner_freq = rand(8193,3);
t = rand(1,15679);
aa_sig_combined = 0;

tic,
for ii=1:1:length(inner_freq)-1
 aa_sig_rebuilt = inner_freq(ii, 2)*cos (2*pi*t*inner_freq(ii, 1) +
inner_freq(ii, 3));
 aa_sig_combined = aa_sig_combined + aa_sig_rebuilt;
end;
toc

Running on Ubuntu 10.04 64bit octave 3.2.4 using i3 processor using 6 gig of ram it takes 6 seconds

Running in a Virtual box Machine using i3 processor Compiled Octave 3.4.2 from source using ubuntu 10.04 32bit using 3gig of ram it takes 9 seconds

On Wed, Oct 5, 2011 at 6:22 AM, Martin Helm <address@hidden> wrote:

Am Dienstag, den 04.10.2011, 16:20 -1000 schrieb Rick T:

> Thanks for all the great help and code I've got it down to 9 seconds
> still get an error "nonconformant arguments (op1 is 1x15679, op2 is
> 8193x1)"
> using the code below but more than likely I would run into memory
> errors latter on down the line since the arrays will only get bigger
> not smaller.
>
>
> clear all
> inner_freq = rand(8193,3);
> t = rand(1,15679);
> aa_sig_combined = 0;
> tic,
> aa_sig_combined2 = sum(inner_freq(:, 2)*cos (2*pi*t.*inner_freq(:, 1)+
> inner_freq(:, 3)));
> toc
>
>
> But 9 seconds is nothing to shake a stick at

I think you misinterpret that result, of course this will give you an
error since you used the _expression_ which was for a scalar t and not the
one which was meant for a non scalar t.

What really surprises me is the 9 sec you mention, using that code it
tells me after a few milliseconds (again this is on a simple netbook!
not on my PC which is roughly 10-20 times faster depending on what is
done) that there is an error. That sounds very strange.

What machine are you running on (RAM, CPU, operating system) and what
octave version?