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From: "John B. Matthews" <nospam@nospam.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Interfacing Ada with C
Date: Thu, 05 Aug 2010 09:23:51 -0400
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Date: 2010-08-05T09:23:51-04:00
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In article 
<b7f5edce-124d-4b91-82f2-e9793d39a3cf@x25g2000yqj.googlegroups.com>,
 Ada novice <posts@gmx.us> wrote:

> 2. a real orthogonal matrix. Such a matrix gives all eigenvalues of
> unit modulus. I tested the case from 
> http://en.wikipedia.org/wiki/Orthogonal_matrix.
> In Matlab,
> 
>    eig([0, -0.8, -0.6; 0.8, -0.36, 0.48; 0.6, 0.48, -0.64])
> 
>    gives the eigenvalues as 0 + 1i, 0 - 1i and -1.
> 
>    Using your Ada code gives:
> 
>    -1.78814E-08  1.00000E+00
>    -8.72890E-09 -1.00000E+00
>    -1.00000E+00  0.00000E+00
> 
> 
> Does the Blas code work with Fortran double-precision? In the above,
> Matlab with double (15 digits precision). I don't see you using the
> type Long_Float in the Ada code. I don't know how many digits are
> being passed from the Fortran result to Ada. Maybe this is causing the
> discrepancy between the expected results (all eigenvalues of modulus
> one) and the output in Ada.

Using these declarations in test_extensions.adb:

   subtype My_Float is Long_Float;

   Input : constant Complex_Matrix
     := (((0.0, 0.0), (-0.8,  0.0),  -0.6,  0.0)),
         ((0.8, 0.0), (-0.36, 0.0),  (0.48, 0.0)),
         ((0.6, 0.0),  (0.48, 0.0), (-0.64, 0.0)));

I get this result:

./test_extensions
 0.00000000000000E+00  1.00000000000000E+00
-2.77555756156289E-17 -1.00000000000000E+00
-1.00000000000000E+00  0.00000000000000E+00

[...]
-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>