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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: Mon, 25 Jun 2012 01:32:30 -0500
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Date: 2012-06-25T01:32:30-05:00
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On 6/25/2012 12:44 AM, J-P. Rosen wrote:
> Le 24/06/2012 19:14, Nasser M. Abbasi a �crit :
>
> If you want to avoid "if" in "loop":
>
>>> 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
>          BI := 1;
>          for AI in A'First (1) .. I-1 loop
>             BJ := 1;
>             for AJ in A'First (2) .. J-1 loop
>                B (BI, BJ) := A (AI, AJ);
>                BJ := BJ + 1;
>             end loop;
>
>             for AJ in J+1 .. A'Last (2) loop
>                B (BI, BJ) := A (AI, AJ);
>                BJ := BJ + 1;
>             end loop;
>             BI := BI + 1;
>          end loop;
>
>          for AI in I+1 .. A'Last (1) loop
>             BJ := 1;
>             for AJ in A'First (2) .. J-1 loop
>                B (BI, BJ) := A (AI, AJ);
>                BJ := BJ + 1;
>             end loop;
>
>             for AJ in J+1 .. A'Last (2) loop
>                B (BI, BJ) := A (AI, AJ);
>                BJ := BJ + 1;
>             end loop;
>             BI := BI + 1;
>          end loop;
>       end return;
>   end Exclude;
>
>


Thanks J-P. Rosen.

Ada is nice as it strongly typed and catches common errors. But
it is not as 'expressive' I am afraid as I'd like for this
sort of thing.

In Mathematica for example, I do this whole operation in one line:

---------------------------
Table[ReplacePart[A,{{i},{i,_},{_,j}}:>Sequence[]],{i,nRow},{j,nCol}];
---------------------------

That is all. This generates all submatrices from A as needed
in this problem :)

I've been learning Mathematica, and I find functional programming
really powerful vs imperative programming, but it needs much more
time getting used to.

But this is for another topic and place to discuss.

Thanks again for your input!

--Nasser