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From: Shark8 <onewingedshark@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: on using array index, vectorized operation
Date: Sun, 27 Mar 2011 14:30:46 -0700 (PDT)
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On Mar 27, 2:44=A0pm, "Nasser M. Abbasi" <n...@12000.org> wrote:
>
> Thanks, Yes, I could I suppose, but it is not really practical.
>
> Is there a way to make
>
> =A0 =A0 =A0 =A0 =A0 A'First .. A'Last
>
> into one variable, say 'i', so I can just write =A0i+1 or i-1 etc..?

No; see Pascal's answer.
I would actually suggest making it even more generic; something along
the lines of:


Subtype Subrange is XXX Range XXX'Succ(XXX'First)..XXX'Last;
or Range XXX'First..XXX'Pred'(XXX'Last); as needed, where XXX is your
index-type.

>Using your solution, I would have to write
>
>u(u'first+1..u'last-1) :=3Du(u'first+1..u'last-1) -
>         (a/2.0)* (u(u'first+2..u'last) - u(u'first..u'last-2))+
>         (a**2)/2.0*  ( u(u'first..u'last-2)-2.0*u(u'first+1..u'last-1) +
>                         u(u'first+2..u'last));

The above could probably* then be rewritten as:

Declare
 SubType SubRange_1 is Natural Range U'Succ(U'First)..U'Pred(U'Last);
 SubType SubRange_2 is Natural Range U'Succ(SubRange_1'First)..U'Last;
 SubType SubRange_3 is Natural Range U'First..U'Pred(SubRange_1'Last);
Begin
  u(SubRange_1):=3D u(SubRange_1) -
      (a/2.0) * ( u(SubRange_2) - u(SubRange_3) ) +
      (a**2)/2.0 * ( u(SubRange_3) - 2.0*u(SubRange_1) +
u(SubRange_2) );
End;

* I didn't run this through my compiler.
I'm sorry about the poor naming of the subtypes, the technical [math]
term escapes me at the moment, but I think it does illustrate what is
going on.