Re: [OctDev] Help making padarray.m quicker

[Paul K. <pki...@us...>]

On Aug 11, 2004, at 4:43 AM, Per Persson wrote:

>
> On Aug 11, 2004, at 04:12, Paul Kienzle wrote:
>
>>
>> On Aug 10, 2004, at 6:18 PM, Josep Mon=E9s i Teixidor wrote:
>>
>>> I've left padding with scalar values as it was in the second version
>>> because, although in my intel box that was slower, as Paul sent
>>> yesterday, that probably makes a real difference on MacOs X.
>>
>> Note the difference in version number: 2.1.55 for OS X,
>> 2.1.57 for linux!  Octave may have changed to make the
>> two more similar.  Does somebody have both versions
>> available on the same system that they can compare?
>
> FWIW, on a 1.25MHz G4 w 512MB RAM iMac with octave 2.1.57 I get (+/- =20=

> 20% accuracy)
>
> octave:1> n=3D800; A=3Dones(n,n);
> octave:2> tic; B=3Dzeros(n+100,n+100); B(51:n+50,51:n+50)=3DA; toc
> ans =3D 0.16152
> octave:3> tic; =20
> =
B=3Dcat(2,zeros(n+100,50),cat(1,zeros(50,n),A,zeros(50,n)),zeros(n+100,50=20=

> )); toc
> ans =3D 0.19956
>
> I don't have any pre-2.1.57 installs, but I'm pretty sure there =20
> weren't any changes between 2.1.55 and 2.1.57 that could justify the =20=

> 10x diff in speed. Did you run the test on a memory starved (which for =
=20
> OS X means <=3D256 MB) system?

octave:12> n=3D200; A=3Dones(n,n);
octave:13> tic; B=3Dzeros(n+100,n+100); B(51:n+50,51:n+50)=3DA; toc
ans =3D 0.045741
octave:14> tic; =20
B=3Dcat(2,zeros(n+100,50),cat(1,zeros(50,n),A,zeros(50,n)),zeros(n+100,50)=
=20
); toc
ans =3D 0.43754

octave:31> n=3D20; A=3Dones(n,n);
octave:32> tic; for i=3D1:10, B=3Dzeros(n+100,n+100); =
B(51:n+50,51:n+50)=3DA; =20
end; toc
ans =3D 0.047229
octave:33> tic; for i=3D1:10, =20
B=3Dcat(2,zeros(n+100,50),cat(1,zeros(50,n),A,zeros(50,n)),zeros(n+100,50)=
=20
); end; toc
ans =3D 0.45311

So I would say the 10x is real.  It's nice to hear that it its gone =20
now.  I just hope that's because cat got faster rather than assignment =20=

getting slower ;-)

Josep, don't worry about choosing an algorithm suitable for older =20
versions of octave.

- Paul=