Re: error: only one index allowed for lists

[Quentin Spencer]

Prasenjit Kapat wrote:

> Hi,
> The subject gives the error message. A toyed down version of what I
> want to do is this..
>
>  
>
> > a = cell(1,3);
> > a{1} = zeros(2,3);
> > a{2} = ones(2,3);
> > a{3} = zeros(2,3);
> > a{:}(1,1)  ## I want this to give [ 0 1 0] as the answer, instead the error...
> >    
> error: only one index allowed for lists
>
> I get what this means. Is there any way around ? To be more fair to my
> problem, I want a 2x3 matrix b = some_function(a) such that, b(i,j) =
> a{1}(i,j) + a{2}(i,j) + a{3}(i,j). Of course, in real terms these
> dimensions are huge, so is the 'length of the list'. Thus the brute
> force way is expensive,O(n^3). Some N-dimensional array, like matlab ?
> Well, I do not have administrative access to the machine, and the
> octave version is an age old one: 2.1.50, possibly on fedora 1.
>  

This type of operation isn't allowed because it really can't be defined 
in any sensible way for cell arrays. The contents of each cell are 
allowed to have different types (string, double, cell, struct, etc), and 
different dimensions. An operation such as the one you suggest would 
make sense for your example, where each element is a matrix of identical 
size, but not for a general cell array. I think your problem definitely 
calls for N-D arrays, which were introduced to Octave shortly after 
2.1.50 if I recall correctly. If you don't have admin access, you might 
try compiling your own copy of octave in your home directory. I've been 
able to make this work successfully before. It does require a lot of 
disk space, though, so that could be problematic if you have 
quotas--maybe you could compile in /tmp.

-Quentin



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