Re: searching for the elegant code (matrix indexing and more)

[Markus Appel]

On 01/23/2014 01:23 PM, oxy wrote:
> hi guys
>
> look at these: i can generate a matrix with all
> possible combinations.
>
>     np=4  % number of parameters. Ex: a, b, c, d
>     m=zeros(0);
>     for l=1:(np-1)
>         m=[m; zeros(np-l,l-1), ones(np-l,1), eye(np-l)];
>     endfor
>
> Now just need to change 0 for : (or 1:dim).
> In other words:
>
> 1   1   0   0   ->  (1, 1, :, :)  for the first row of matrix m.
>
> I'm struggling but dont find a way!
>
> thx for your creative support!
>
> ps: hey markus, i didnt get your point yet ...
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The code I posted earlier avoids the problem you have, the sig matrix
gets permuted (i.e. the dimensions are rearranged) and then the two
first ones are selected by (:,:,1,1,1). The loops run through all
possible combinations.

If you want to do it your way, have a look at the function subsref. For
example, if you would like to index your matrix sig with the first row
of matrix m by replacing 0 with : , you would do:

idx.type = '()'
idx.subs = cellfun( @(x) ifelse(x==0,":",x), num2cell(m(1,:)),
'UniformOutput', false)
submatrix = squeeze(subsref(sig,idx))

Markus