From help-request at octave dot org Sat Oct 15 14:38:13 2005
Subject: Re: error "can't perform indexing operations for <unknown type> type"
From: David Bateman <David dot Bateman at motorola dot com>
To: cmire <gnuguy at thelink dot net>
CC: help at octave dot org
Date: Sat, 15 Oct 2005 21:32:24 +0200

cmire a écrit :

>I'm new to Octave, and I've got a short Matlab program from a professor that 
>we are supposed to modify to solve some homework problems.  I've read that 
>Octave can run Matlab code (I've updated the ~/octaverc file accordingly, 
>etc.).
>
>When I try to run the code using the command "source(Exercise.m)", I get the 
>output:
>
>length = 10
>npoints = 200
>mass = 0.070000
>num_sol = 4
>error: can't perform indexing operations for <unknown type> type
>error: evaluating argument list element number 1
>
>I don't need help with the actual homework assignment -- I just need to get 
>this code working so I can proceed to do my homework.  Help is greatly 
>appreciated!
>
>  
>
Not sure why there is this error, and is certainly a bug in the version 
of octave you are using as it indicates that an uninitalized value is 
being returned from a compiled function, might be due to issues with eigs..

In any case the only version of eigs that exists for octave is the one I 
have that has serious stability problems and only works (and then just) 
for real symmetric marices. So I haven't made this version of eigs 
available. You therefore have two choices. 1) Forget trying to use 
octave for this code, or
2) change the eigs call to read something like

[phi,te] = eig(Hmatrix);
[te, idx] = sort(Hmatrix);
te = te(1:num_sol);
phi = phi(:,idx(1:num_sol));

though for large matrices and small num_sol this will be significantly 
slower than using eigs as all of he eigenvectors are calculated and you 
only pick num_sol of them.

D.



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
-------------------------------------------------------------