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From: "Nasser M. Abbasi" <nma@12000.org>
Newsgroups: comp.lang.ada
Subject: Re: Any easy/build-in construct to extract submatrices from larger
 matrix?
Date: Sun, 24 Jun 2012 12:14:11 -0500
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Date: 2012-06-24T12:14:11-05:00
List-Id: <comp.lang.ada>

On 6/24/2012 11:11 AM, Dmitry A. Kazakov wrote:
> 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.
>

Yes, I am sure of this. But it is just for learning purposes.

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

Thanks, Will try it out! You are good in Ada, so can write functions
like this as needed quickly. I think Ada should add more
support for more build-in type functions for matrix/vector operations.

At least, 2D slicing of arrays should be possible? If not, that
mask/pack functionality as in Fortran, should be present in Ada
as part of the library.

> 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;
>

Thanks again for the function. If I use it in my engineering
HOWTO cheat sheet, will put your name as the credit on it.

regards,
--Nasser