Re: Significant speed-up of datevec

[Jaroslav Hajek]

On Thu, Dec 18, 2008 at 5:33 AM, Daniel J Sebald <address@hidden> wrote:
> Attached is a patch to significantly speed up datevec() in the case that a
> string matrix or string cell is passed in.  The ~50 speedup comes simply
> from only deciphering the format string once instead of for every entry in
> the cell/string matrix.  Here is a test function:
>
> function DN = testfunc4()
>  date1 = '2008-12-16 22:12:00';
>  D = repmat(date1, 1000, 1);
>  tstart = cputime();
>  DN = datenum(D, 'yyyy-mm-dd HH:MM:SS');
>  cputime - tstart
> end
>
> and results, without the patch:
>
> octave:1> DN = testfunc4();
> ans =  70.594
>
> with the patch:
>
> octave:1> DN = testfunc4();
> ans =  1.4648
>
> There are probably other little things that could be done to save some time,
> but this gets the bulk of it.
>
> What I don't understand though, is that successively calling this test
> function results in worse performance after the first call:
>
> octave:2> DN = testfunc4();
> ans =  2.1877
> octave:3> DN = testfunc4();
> ans =  2.2437
> ...
>
> Any ideas?  (I check the usual suspects, like having to delete the return
> value, etc.)
>

Not really. I have, however, noted that "clear all" prevents the
effect, so I suspect some problem with persistent variables. But it's
definitely worth further investigation.

> Dan
>

I applied this patch. If you intend to make more than a few
contributions to Octave, please consider making yourself familiar with
Mercurial and then using it to create, organize and send patches.

thanks

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