Re: Interfacing Ada with C

[Ada novice <posts@gmx.us>]

Many thanks for all your inputs. I'll give you an example. Say we want
to compute the eigenvalues of this 3 X 3 matrix. The code in C (using
the IMSL library) is as follows:

#include <imsl.h>

int main()
{
int n = 3;
float a[] = {8.0, -1.0, -5.0,
-4.0, 4.0, -2.0,
18.0, -5.0, -7.0};
f_complex *eval;
/* Compute eigenvalues of A */
eval = imsl_f_eig_gen (n, a, 0);
/* Print eigenvalues */
imsl_c_write_matrix ("Eigenvalues", 1, n, eval, 0);
}


and the output on the screen (with some pretty formatting from
imsl_c_write_matrix) is:

       Eigenvalues
     1        2        3
( 2, 4) ( 2, -4) ( 1, 0)

Here, the first eigenvalue is 2 + 4i, the second one is 2 -4i and so
on. I found that f_complex (used in the line f_complex *eval) is
defined as follows:

typedef struct{
float re;
float im;
} f_complex;

and f_complex is for single-precision complex values (d_complex exists
for double-precision).

I have never worked with structures before and after some
"cursing" :), I could access the individual elements as follows:

printf(" %g\n", eval[0].re) will give me the real part of the first
eigenvalue i.e. 2.

What would the best way to interface this with Ada? The elements of my
matrix will be formed in Ada, then the matrix will be passed to C to
calculate the eigenvalues and then the latter passed back to Ada. The
size of my matrix will be fixed say 3 x 3. As a novice in Ada, I would
like to learn good programming practice and the best way is to use
codes and learn from experts here in Ada.

Thanks for your very kind help.
YC