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From: 18k11tm001@sneakemail.com (Russ)
Newsgroups: comp.lang.ada
Subject: Re: Is ther any sense in *= and matrices?
Date: 7 Jun 2003 12:38:40 -0700
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Preben Randhol <randhol+abuse@pvv.org> wrote in message news:<slrnbdupg6.88r.randhol+abuse@kiuk0152.chembio.ntnu.no>...
> Vinzent Hoefler wrote:
> > Preben Randhol wrote:
> > 
> >>Vinzent Hoefler wrote:
> >>> Of course it is. But because you have to write the Multiply function
> >>> yourself anyway and such can take care of that issue, I don't see why
> >>> this should be a problem. 
> >>
> >>Because it doesn't make sense mathematically.
> > 
> > Dividing by zero doesn't make sense either. So IMO that's what the
> > Constraint_Error is for.
> 
> The Contraint_Error here is for that *= would return a C (m x n) which
> differes from the A (n x n). So *= is only usefule (/= too) in special
> cases such as square matrix. Therefore you must make a function Prod
> (A,B) at any rate and the *= will be of no use as Prod (A,B) is
> general.

"*=" is not so useful for multipying non-square matrices. However, it
is very useful for multiplying a matrix (or a vector) by a scalar. For
example,

    A *= 2.0

can be used to multiply matrix A by two in place. This is potentially
more efficient than A := A * 2 for all the same reasons discussed with
respect to "+=".