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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Any easy/build-in construct to extract submatrices from larger
 matrix?
Date: Sun, 24 Jun 2012 18:11:27 +0200
Organization: cbb software GmbH
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Date: 2012-06-24T18:11:27+02:00
List-Id: <comp.lang.ada>

On Sun, 24 Jun 2012 07:16:50 -0500, Nasser M. Abbasi wrote:

> On 6/24/2012 6:10 AM, Dmitry A. Kazakov wrote:
> 
>> And to me the problem is not clear. Are you writing a concrete program or
>> considering a proper way to model matrix lattices in a strongly typed
>> programming language? The difference is huge.
>>
> I was try to implement, just for fun, finding the adjungate
> matrix, using the direct algorithm using Ada, as shown here:
> 
> http://en.wikipedia.org/wiki/Adjugate_matrix
> 
> it requires finding the cofactors of each element in a 2D matrix.

I suppose that there exist much better numerical methods than doing this as
described in the definition.

> Hence needed a simply way to obtain a submatrix from the main
> matrix.

If you want a function which would return a submatrix obtained by removing
the row I and column J:

function Exclude (A : Complex_Matrix; I, J : Integer)
   return Complex_Matrix is
   AI, AJ : Integer := A'First (1);
begin
   return B : Complex_Matrix (1..A'Length (1)-1, 1..A'Length (2)-1) do
      AI := A'First (1);
      for BI in B'Range (1) loop
         if AI = I then
            AI := AI + 1;
         end if;
         AJ := A'First (2);
         for BJ in B'Range (2) loop
            if AJ = J then
               AJ := AJ + 1;
            end if;
            B (BI, BJ) := A (AI, AJ); 
            AJ := AJ + 1;
         end loop;
         AI := AI + 1;
      end loop;
   end return;
end Exclude;

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