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From: "Alexander Boucke" <alexb@lufmech.rwth-aachen.de>
Newsgroups: comp.lang.ada
Subject: Re: efficient vector/matrix operations in Ada
Date: Tue, 14 Aug 2001 10:17:22 +0200
Organization: Lehr- und Forschungsgebiet f. Mechanik
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> > 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.


There is a way to do the same (regarding efficiency) in Ada 95 using the A:=
B + C + D form. For my work I've written a Matrix-Vector package, that
encapsulates the Arrays using access-types. The only temporary objects you
get now are access-types. There would have been a problem with the RAM
slowly filling up, so I used controlled types to do reference-counting.
Together with a temporary vector holding all results from sums, this leads
to equivalent efficiency as using the += operators. You have to deal with
the overhead due to the garbage collection using controlled types, but that
is negligible when using large vectors/matrices as in typical finite element
programs.

How this could look (simplified):

package vectors is

...

  type Vector is new Ada.Finalization.Controlled with private;

  function "+" (left,right : vector) return vector;

...

private

  type value_array is array (<>) of real;
  type handled_vector (first,last : integer) is
     record
        value : value_array(first, last);
        count : natural; -- for reference counting
     end record;

  type handled_vector_access is access handled_vector;

  type vector is new ada.finalization.controlled with
     record
        the_vector : handled_vector_access;
     end record;

end vectors;


Regards,

Alexander Boucke