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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: ANN: Ada 2005 Math Extensions, 20100810 release
Newsgroups: comp.lang.ada
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Date: Sat, 14 Aug 2010 22:48:43 +0200
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Date: 2010-08-14T22:48:43+02:00
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On Sat, 14 Aug 2010 20:16:31 +0100, Simon Wright wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> On Sat, 14 Aug 2010 17:26:20 +0100, Simon Wright wrote:
>>
>>> Given that, the function taking Complex_Matrix and returning
>>> Complex_Vector has "obviously" to be in a child of
>>> Generic_Complex_Arrays.
>>> 
>>> So I thought that the function taking Real_Matrix should be in a child
>>> of Generic_Real_Arrays, in spite of the fact it returns a Complex_Vector.
>>> 
>>> Clearly this is not the way Nature intended!
>>
>> Hmm, a complex valued function is complex to me. Consider exp(jwt). The
>> argument is real t, the result is complex. Where does it belong?
> 
> I think maybe I'll meet Stephe halfway: Ada.Numerics.Generic_Arrays!
> 
> Another problem, of course .. Ada 2017 might implement something in this
> space.

If you don't make it a child you can leave the Ada's name space:

   package Linear_Algebra.Generic_Eigenvaues_Problem

or something alike.

Regarding Stephe's proposal, independently on the package name you use, I
would suggest this:

with Ada.Numerics.Generic_Complex_Arrays;
generic
   with package Complex_Arrays is
      new Ada.Numerics.Generic_Complex_Arrays (<>);
package Whatever is
   use Complex_Arrays;
   use Complex_Types;  -- Complex_Arrays.Complex_Types
   use Real_Arrays;        -- Complex_Arrays.Real_Arrays

   function Eigenvalues (A : Real_Matrix) return  Complex_Vector;
end Whatever;

You do not need to pass all chain of Generic_Complex_Arrays' arguments,
instead you pick its parameter. This technique greatly simplifies
instantiations.

BTW, this is exactly the case where you might like to rename Complex_Arrays
and others. These unnatural names xxx_Of! (:-)) I am not sure if renaming
is still actual, but it was necessary before. And I have no idea if that
was because of a compiler or language design bug.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de