From help-request at octave dot org Sat Jan 15 17:01:25 2005
Subject: Re: Very slow filter.cc
From: David Bateman <David dot Bateman at motorola dot com>
To: akira at rsch dot tuis dot ac dot jp, help@octave.org
Date: Sun, 16 Jan 2005 00:03:27 +0100


Hi Akira,

akira at rsch dot tuis dot ac dot jp wrote:

>I recently begin to use the development version of octave (2.1.64) and
>found that filter function is very slow compared with that of
>octave-2.0.17.
>
>The test code I attached the last part of this mail showed that the
>new filter function (2.1.64) is 9 times slower than the old filter
>function (2.0.17). I converted codes executing actual filtering from
>the old filter.cc to the new filter.cc, it made five times faster than
>the new filter.cc of 2.1.64. It still twice slower than the old filter
>function. The rest of the new filter.cc may be codes for input, output
>and error handling and I was not able to figure out the problem.
>
>I suspect that the reason of slow filter function is NDArray support
>for
>the third and fourth arguments of the filter function. The speed of
>filter function should be very critical for users of digital signal
>processing and I want to say goodby to the slow filter function.
>
>I compiled octave-2.1.64 with ATLAS-3.6 and FFTW-3.0.1. Please tell me
>the way to speed up filter function.
>  
>

I'd taken note of this an had hoped to investigate the problem a little, 
as if as you suspect the problem is due to the conversion to NDArray's 
then its my fault as I wrote that code. However, it seems unlikely I'll 
have any time to look at this soon, and hope you might be able to 
investigate further...

What was going to be my first step was to compile three different 
versions of octave.
These being 2.1.50, 2.1.57 and 2.1.64, which correspond to the last 
three testing releases. The first before NDArray's were integrated, the 
second when NDArray's were integrated, but the filter function wasn't 
changed to use them and the last with the filter function converted to 
NDArray's. Getting the times of the test case you propose for these 
three build, would really confirm your problem.

I can't promise to do anything with this information rapidly, so feel 
free to search for a better implementation of an NDArray filter function 
if you do indeed confirm that this is the base problem. However, if you 
don't do it, I'll eventually get araound to it, at least before the 
magical version 3.0 release :-)

Regards
David


>==== test code 1 ====
>
>x = randn(1e6,1); b = randn(500,1);
>tic, y = filter(b, 1, x); toc
>
># AthlonXP 2200+ octave-2.1.64 Linux-2.4.27
>ans = 14.712
>
># AthlonXP 2200+ octave-2.0.17 Linux-2.4.27
>ans = 1.6280
>
>==== test code 2 ====
>
>x = randn(1e5,10); b = randn(500,1);
>tic, y = filter(b, 1, x); toc
>
># AthlonXP 2200+ octave-2.1.64 Linux-2.4.27
>ans = 14.430
>
># Multi-dimensional array does not contribute its speed!!
>
>==== test code 3 ====
>
>x = randn(1e5,10); b = randn(500,1);
>tic, for k=1:10
>y(:,k) = filter(b, 1, x(:,k));
>end; toc
>
># AthlonXP 2200+ octave-2.0.17 Linux-2.4.27
>ans = 1.7135
>
>_/_/_/  _/  _/            _/            _/_/        Akira NISHIMURA
> _/    _/  _/            _/             | Dept. of Media and Cultural Studies
>_/okyo _/_/niversity of _/nformation _/_/ciences akira at rsch dot tuis dot ac dot jp
>                   http://www.rsch.tuis.ac.jp/~akira
>
>
>
>
>
>
>
>
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>
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>  
>


-- 
David Bateman                                David dot Bateman at motorola dot com
Motorola CRM                                 +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 1 69 35 77 01 (Fax) 
91193 Gif-Sur-Yvette FRANCE

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