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From: 18k11tm001@sneakemail.com (Russ)
Newsgroups: comp.lang.ada
Subject: Re: efficient vector/matrix operations in Ada
Date: 13 Aug 2001 12:45:43 -0700
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B_Gaffney@My-Deja.com (B.Gaffney) wrote in message news:<9f6e2b77.0108100854.66b084b4@posting.google.com>...
> "Russ P." <18k11tm001@sneakemail.com> wrote in message news:<3B6F5ABC.3C40E189@sneakemail.com>...
> > No, you really need the dynamically instantiated temporary matrix, I
> > believe. I've been through this little lesson years ago. Don't forget
> > that you also need to be able to handle expressions such as "A = B + C +
> > D;". You can play complicated games with static arrays of "work"
> > matrices, but you are asking for trouble and the resulting code is
> > likely to not be re-entrant.
> 
> Um, OK, but how would you handle this case using your "+="
> implementation?  That was your original point wasn't it?
> 
>                        --Bg

Here's how you write "A = B + C + D;" efficiently:

    A  = B;
    A += C;
    A += D;

This requires no temporary matrices or passing by value. The original
form (A=B+C+D) is fine for rapid prototyping, but the efficient form
is preferable for production code. As far as I am concerned, Ada
really needs arithmetic assignment operators. Sure, you can use
procedures, but they're intent and effect is not as obvious to the
reader.

Russ