From bug-request at octave dot org Wed May 18 08:08:21 2005
Subject: version 2.1.69 under mac OS X: randn does not work properly
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: =?ISO-8859-1?Q?Sa=EFd?= <ladjal at enst dot fr>
Cc: bug at octave dot org
Date: Wed, 18 May 2005 09:04:43 -0400

On 18-May-2005, Sa=EFd wrote:

| Hi,
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|   I am using the version 2.1.69 of octave under mac OS X 10.3.9,=20
| (hardware: iBook G4). I downloaded the binary version from:
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| http://hpc.sourceforge.net/
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| It seems to have a very serious bug affecting the gaussian random=20
| generator:
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| Here is an example
| ----------------------------
| dhcp132-235-~ $ octave
| GNU Octave, version 2.1.69 (powerpc-apple-darwin7.8.0).
| Copyright (C) 2005 John W. Eaton.
| This is free software; see the source code for copying conditions.
| There is ABSOLUTELY NO WARRANTY; not even for MERCHANTIBILITY or
| FITNESS FOR A PARTICULAR PURPOSE.  For details, type `warranty'.
|=20
| Additional information about Octave is available at=20
| http://www.octave.org.
|=20
| Please contribute if you find this software useful.
| For more information, visit http://www.octave.org/help-wanted.html
|=20
| Report bugs to <bug at octave dot org> (but first, please read
| http://www.octave.org/bugs.html to learn how to write a helpful repor=
t).
|=20
| octave:1> x=3Drandn(1,10000);
| octave:2> sum(x>3)
| ans =3D 4001
| ------------------
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| Using a proper random generator, the last answer would have been more=
=20
| like 10.
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|   I also use the version 2.1.53 (from the Fink project) which does no=
t=20
| have this problem.
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|   Workaround:
|      You can replace:
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|     x=3Drandn(1,N);
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| by
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|   x=3Dsum(rand(12,N)-0.5);
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|   to get a nearly-gaussian distribution.

There are unfortunately different versions of rand for Octave.  If you
have installed octave-forge, then you are getting the alternate
version, which appears to have the bug (may already be fixed in the
CVS sources, I don't know).  But the version that is distributed as a
part of Octave does not appear to have the problem.

jwe



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