Re: stack and append

[Eduardo Gallestey]

heberf wrote:
> 
> I need a faster implementation of the kronecker product.  The one that comes
> with octave is in linear-algebra/kron.m and it's not suitable for me because 
> my
> problem involves many large matrices.  I'm trying to rewrite it as an oct 
> file.
> 
> A few weeks ago there was some discussion on this list of using stack and 
> append
> as defined in dMatrix.h.  I'm pretty poor at C++ and I can't tell from reading
> that file how to implement it.  Could someone point out a function where 
> either
> of these are used or send a few lines of an oct file so I can see how to do 
> it?
> 
> Much thanks,
> Heber Farnsworth
> 
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I have a general question with respect to that. Maybe I am wrong but,
wouldn't it be more efficient if we allocate all the space for "x" at
once, at the beginning of the function? I mean, like this:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

function x = mykron (a, b)

  if (nargin == 2)

    [m, n] = size (b);
    [ma, na] = size (a);

    x=zeros(ma*m,na*n); 

    for jj = 1:na
      j_vec=n*(jj-1)+1:n*jj;
      for ii = 1:ma
        x(m*(ii-1)+1:m*ii,j_vec) = a(ii,jj)*b;;
      endfor
    endfor

  else
    usage ("kron (a, b)");
  endif

endfunction

%%%%%%%%%%%%%%%%%%%%%%%%%

Eduardo



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