Re: memory management on Octave + writing .oct files

[Agnes Bousquier]

Hello,

 Thank you very much to J.W Eaton and Q.Spencer for their replies.
 In fact, I have to read frames coming from a .avi file in my program, 
so I wrote the Octave script "testaviread.m" to test two ways of doing it:
_ uncommenting the lines 5 to 7 (the "for" loop) and commenting the line 
10 (testavirec(1,50);) will make Octave read the frames thanks to a 
"for" loop; in fact, this solution is slow, but do not use much memory 
on my Windows XP system;
_ in the other hand, I call the function "testavirec"; it reads the 
frames on a recursive way, and so is supposed to run faster than a "for" 
loop. But the problem is that when my function reads the (k+1)th frame, 
it does not delete the kth from the memory, and so my system slows 
down... Finally  this method is slower than the first because of this 
memory management problem; but maybe is this issue due to the fact that 
I use Octave under Cygwin, and so it has no "real" access to virtual 
memory?

Best regards,

Agnes

Quentin Spencer a écrit :
> Agnes Bousquier wrote:
>
> > Hello everybody,
> >
> >   I am facing problems of slowness with my .m files, so I tried 
> > several ways to make them run faster, and have some questions :
> >
> > 1- Are there any routines which allows us to manage memory on Octave 
> > (like "malloc" and "free" for C language)?
>
> If you want to pre-allocate arrays (which does increase speed in some 
> cases), simply create an array of the correct dimensions using the 
> zeros command. Using the "clear" command will clear an array from 
> memory, and so is roughly equivalent to "free".
>
> > 2- About .oct files : what should I do to call an Octave's function 
> > (like imshow) in a .oct file?
> I don't know if it works for m files, but if you have another oct file 
> function called func, you can call it from C using Ffunc.
>
> Another general comment about speed in octave: make sure you are using 
> vector functions where possible to avoid for loops. Seeing ways to do 
> so takes a lot of familiarity with the language--some of the functions 
> I wrote in the first years after I learned Matlab were much slower 
> than they could have been. If you have specific examples of code that 
> is slow, you could see if anyone here knows ways to make it faster.
>
> -Quentin
>
>
>
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Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
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