Re: error "can't perform indexing operations for <unknown type> type"

[David Bateman]

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.



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