On Thu, Mar 31, 2011 at 8:39 AM, Vic Norton
<address@hidden> wrote:
I have compared the speed of the instructions "norm(x)" and
"sqrt(sum(x .* x))" on Thomas Treichl's Octave.app (3.2.3) and Julien
Salort's Octave.app (3.4.0). These versions of octave can be found at
http://sourceforge.net/projects/octave/files/Octave%20MacOSX%20Binary/
2011-03-27 binary of Octave 3.4.0 (2011-03-27)
2009-10-03 binary of Octave 3.2.3 (2010-11-23)
Here is a summary of the results I observed.
1. Octave 3.4.0 is a bit slower than Octave 3.2.3 on sqrt(sum(x .* x)).
2. On Octave 3.2.3, norm(x) is a bit faster than sqrt(sum(x .* x)). This
is as it should be since NRM2 is a BLAS.
3. On Octave 3.4.0, sqrt(sum(x .* x)) is four times as fast as norm(x).
This is not as it should be for the reason cited in 2.
4. norm(x) on Octave 3.2.3 is nine times as fast as norm(x) on Octave
3.4.0.
My test script and my results appear below.
Regards,
Vic
The test script. The two different shebang lines placed at the top
test the two different versions of octave.
#!/usr/local/bin/octave323
# norm2test.m
#!/usr/local/bin/octave323
#!/usr/local/bin/octave340
ntests = 20; n = 1e6; x = rand(n, 1);
test1 = zeros(ntests, 1); test2 = zeros(ntests, 1);
for i = 1 : ntests
tic;
norm(x);
test1(i) = toc;
endfor
for i = 1 : ntests
tic;
sqrt(sum(x .* x));
test2(i) = toc;
endfor
printf ("norm2 speed test - octave %s\n", version);
printf ("%40s\n","ellapsed times");
printf ("%30s%10s\n", "mean", "stdv");
printf ("%-20s", "norm(x)");
printf ("%10.2e", mean(test1));
printf ("%10.2e", std(test1));
printf ("\n");
printf ("%-20s", "sqrt(sum(x .* x))");
printf ("%10.2e", mean(test2));
printf ("%10.2e", std(test2));
printf ("\n");
The output.
---
GNU Octave, version 3.2.3
Copyright (C) 2009 John W. Eaton and others.
This is free software; see the source code for copying conditions.
There is ABSOLUTELY NO WARRANTY; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. For details, type `warranty'.
Octave was configured for "i386-apple-darwin8.11.1".
Additional information about Octave is available at http://www.octave.org.
Please contribute if you find this software useful.
For more information, visit http://www.octave.org/help-wanted.html
Report bugs to <address@hidden> (but first, please read
http://www.octave.org/bugs.html to learn how to write a helpful report).
For information about changes from previous versions, type `news'.
norm2 speed test - octave 3.2.3
ellapsed times
mean stdv
norm(x) 7.06e-03 2.62e-05
sqrt(sum(x .* x)) 1.06e-02 1.98e-03
---