From octave-sources-request at bevo dot che dot wisc dot edu  Fri Oct 15 12:58:43 1999
Subject: builtin kron function.
From: etienne grossmann <etienne at anonimo dot isr dot ist dot utl dot pt>
To: octave-sources at bevo dot che dot wisc dot edu
CC: etienne at isr dot ist dot utl dot pt
Date: Fri, 15 Oct 1999 18:59:34 +0100 (WEST)



  Hello,

  I added to 'data.cc' a 'kron2' function that implements the
Kronecker product (assuming real matrices). It came out to be just
barely faster than the 'mykron' function I sent earlier today, I
wonder why.

  The function is built around a double loop, where 'a','b' are the
input and 'c' is the output.

  Matrix c (rc,cc) ;
  for( i=0,ia=-1; i<rc; i++ ) {
    i%rb || ia++ ;
    for( j=0,ja=-1; j<cc; j++ ) {
      j%cb || ja++ ;
      c(i,j) = a(ia,ja) * b( i % rb, j % cb ) ;
    }
  }

  I can use c.elem(i,j) instead of c(i,j), but that does not improve
things. Would there be a way of accessing "more directly" to the
elements? 

  Cheers,

  Etienne


ps : Why does 'make' in "src" cause 'octave' to be rebuilt even if
     nothing has been touched?

pps: Does it sound like a good idea to rewrite the 'reshape' function
     as a builtin?