Re: Unidentified subject!

[Paul Kienzle]

On Mar 27, 2004, at 8:58 AM, Antonio L. wrote:

> Hello, mi problem can be split into two separated topics:
> - Is there a more efficient way of doing this? (that is, without 'for' 
> looping):
>
>         for i=1:n
>                 M(I(n,1),J(n,1)) = V(n,1);
>                 endfor;
>
> Where V,I,J are nx1 vectors, and M is a nxm matrix? Suposing indexing 
> M with
> values contained in vectors I and J is always possible.
> It should be obvious that the best way for doing so would simply be
>
>         M(I,J) = V;
>
> but octave doesn't works like that.

M(I+(J-1)*rows(M)) = V;

or maybe

M(sub2ind(size(M),I,J)) = V;

> - Supposing we can do that, what about dealing with the case where 
> [I,J] values
> could index cells outside the given matrix? Just like the code below:
>
>         for i=1:n
>                 for j=1:m
>                         if ( (0<i<=rows(M)) && (0<j<=columns(M)) )
>                                 M(i,j) = M2(I(i,j),J(i,j));
>                         else
>                                 M(i,j) = value;
>                         endfor;
>                 endfor
>
> Where M, I, J are nxm matrices, and M2 is a general matrix. Is there an
> efficient and elegant solution, preferredly avoiding 'for' loops?

M = value*ones(m,n);
valid= (0<i<=rows(M2)) & (0<j<=columns(M2))
M(I(valid)+(rows(M)-1)*J(valid))=M2(I(valid)+(rows(M2)-1)*J(valid));

Paul Kienzle
address@hidden



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