Re: indexing expression performance

[Jaroslav Hajek]

On Thu, Jan 15, 2009 at 1:48 PM, Francesco Potortì <address@hidden> wrote:
> I had written:
>>>Also, Francesco, I forgot to do the obvious thing and test your examples
>>>with 3.1.51. At least on my machine, it looks like the performance has been
>>>reversed by the latest dense indexing improvements.
>>>
>>>octave:1> kk=rand(156,222,1,44,8);
>>>octave:2> t=cputime; for ii=1:44, for jj=1:8, mm=kk(:,:,:,ii,jj); endfor,
>>>endfor, cputime-t
>>>ans =  0.072004
>>>octave:3> cp=[1,cumprod(size(kk)(1:end-1))]; len=156*222; t=cputime; for
>>>ii=1:44, for jj=1:8,base=sum(([1,1,1,ii,jj]-1).*cp); mm=kk(base+1:base+len);
>>>endfor, endfor, cputime-t
>>>ans =  0.12401
>>
>>Wonderful!  This will make my code more readable as soon as I upgrade :)
>
> Hm.  I installed Octave 3.1.51 from Debian's "experimental" (I never got
> round to finding the time to build Octave myself).  I use an amd64 box.
> Unfortunately, I see no big difference with 3.0.1 :(
>
> The timings of the first test versus the second on my box are:
> - 5.1s versus 0.30s with 3.0.1
> - 5.2s versus 0.27s with 3.1.51
>
> So apparently I am not benefitting from the 3.1.51 dense indexing 
> improvements.
>

The dense indexing improvements started with
http://hg.savannah.gnu.org/hgweb/octave/rev/7cbe01c21986
dated 20th October and lots of bugfixes afterwards. I don't think this
was in the 3.1.51 snapshot which I think was done in late July. There
was no 3.1.52 so far. So, if you want these, development sources are
your only resort.

regards

-- 
RNDr. Jaroslav Hajek
computing expert
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz