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From: "Nasser M. Abbasi" <nma@12000.org>
Newsgroups: comp.lang.ada
Subject: basic question on adding 2 arrays
Date: Sat, 12 Jul 2014 22:34:53 -0500
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Xref: news.eternal-september.org comp.lang.ada:20899
Date: 2014-07-12T22:34:53-05:00
List-Id: <comp.lang.ada>

I am really rusty in Ada since I have not used it for sometime.

Is there an easy way to add one slice of an array to another
without having to make an explicit loop?  Here is MWE

------------------------------------------------
with Ada.Text_IO;                       use Ada.Text_IO;

procedure foo is
    nPoints : constant Integer := 100;
    type grid_type is array (1 .. nPoints) of Float;
    now : grid_type := (others => 0.0);
    next: grid_type := now;
    begin
      next(2..now'length-1) := 1/2*
        (now(1..now'length-1)+now(3..now'length));
end foo;
--------------------------------------------------

I am basically trying to update an array (this is a finite difference
scheme).  The error is that "+" is not defined for the grid_type,
which I understand ofcourse. But wanted to ask if there is a way
to do this in-line without having to define a method for this.

For example, in Matlab or Fortran something like this works:

    next(2:end-1) = 1/2*(now(1:end-2)+now(3:end));

It is not big deal to defined "+" for the grid_type, but
wanted to check if there might be a way to do it without,
or a better way to do update.

thanks,
--Nasser