matmultodiagonal

Function: matmultodiagonal
Section: linear_algebra
C-Name: matmultodiagonal
Prototype: GG
Help: matmultodiagonal(x,y): product of matrices x and y, knowing that the
 result will be a diagonal matrix. Much faster than general multiplication in
 that case.
Doc: product of the matrices $x$ and $y$ assuming that the result is a
 diagonal matrix. Much faster than $x*y$ in that case. The result is
 undefined if $x*y$ is not diagonal.