Re: help requested with extremely slow for loop?

[Carlo de Falco]

On 24 Mar 2010, at 11:22, Joachim De Beule wrote:

>         octave> idxs = find(x & y);
>         octace>
>         tic
>         for j = idxs
>                 x(y(j)) += x(j);
>                 x(j) = 0;
>         endfor
>         toc
>
>         octave> Elapsed time is 15.96 seconds.
>
> Does anybody have an idea what is going on here or have suggestions  
> about how
> to do this differently? Basically, y(j) holds the new j' that should  
> get the
> value of x(j), after which x(j) itself needs to be set to zero...

what about the following?

idxs = find (x & y);
x(y(idxs)) += x(idxs);
x(idxs)=0;

I haven't actually tested it but it should do the same as your code...
you might also want to try:

idxs = (x & y);
x(y(idxs)) += x(idxs);
x(idxs)=0;

> Thanks!
>
> Joachim.


HTH,
c.