```/* nag_real_sym_posdef_packed_lin_solve (f04bec) Example Program.
*
* Copyright 2014 Numerical Algorithms Group.
*
* Mark 8, 2004.
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nagf04.h>
#include <nagx04.h>

int main(void)
{
/* Scalars */
double        errbnd, rcond;
Integer       exit_status, i, j, n, nrhs, pdb;

/* Arrays */
char          nag_enum_arg;
double        *ap = 0, *b = 0;

/* Nag Types */
NagError      fail;
Nag_OrderType order;
Nag_UploType  uplo;

#ifdef NAG_COLUMN_MAJOR
#define A_UPPER(I, J) ap[J*(J-1)/2 + I - 1]
#define A_LOWER(I, J) ap[(2*n-J)*(J-1)/2 + I - 1]
#define B(I, J)       b[(J-1)*pdb + I - 1]
order = Nag_ColMajor;
#else
#define A_LOWER(I, J) ap[I*(I-1)/2 + J - 1]
#define A_UPPER(I, J) ap[(2*n-I)*(I-1)/2 + J - 1]
#define B(I, J)       b[(I-1)*pdb + J - 1]
order = Nag_RowMajor;
#endif

exit_status = 0;
INIT_FAIL(fail);

printf("nag_real_sym_posdef_packed_lin_solve (f04bec) Example "
"Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%ld%ld%*[^\n] ", &n, &nrhs);
if (n > 0 && nrhs > 0)
{
/* Allocate memory */
if (!(ap = NAG_ALLOC(n*(n+1)/2, double)) ||
!(b = NAG_ALLOC(n*nrhs, double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
#ifdef NAG_COLUMN_MAJOR
pdb = n;
#else
pdb = nrhs;
#endif
}
else
{
printf("%s\n", "n and/or nrhs too small");
exit_status = 1;
return exit_status;
}
scanf("%39s%*[^\n] ", nag_enum_arg);

/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
uplo = (Nag_UploType) nag_enum_name_to_value(nag_enum_arg);

/* Read the upper or lower triangular part of the matrix A from */
/* data file */

if (uplo == Nag_Upper)
{
for (i = 1; i <= n; ++i)
{
for (j = i; j <= n; ++j)
{
scanf("%lf", &A_UPPER(i, j));
}
}
scanf("%*[^\n] ");
}
else
{
for (i = 1; i <= n; ++i)
{
for (j = 1; j <= i; ++j)
{
scanf("%lf", &A_LOWER(i, j));
}
}
scanf("%*[^\n] ");
}

/* Read B from data file */
for (i = 1; i <= n; ++i)
{
for (j = 1; j <= nrhs; ++j)
{
scanf("%lf", &B(i, j));
}
}
scanf("%*[^\n] ");

/* Solve the equations AX = B for X */
/* nag_real_sym_posdef_packed_lin_solve (f04bec).
* Computes the solution and error-bound to a real symmetric
* positive-definite system of linear equations, packed
* storage
*/
nag_real_sym_posdef_packed_lin_solve(order, uplo, n, nrhs, ap, b, pdb,
&rcond, &errbnd, &fail);
if (fail.code == NE_NOERROR)
{
/* Print solution, estimate of condition number and approximate */
/* error bound */

/* nag_gen_real_mat_print (x04cac).
* Print real general matrix (easy-to-use)
*/
fflush(stdout);
nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
nrhs, b, pdb, "Solution", 0, &fail);
if (fail.code != NE_NOERROR)
{
printf("Error from nag_gen_real_mat_print (x04cac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
printf("\n");
printf("%s\n%6s%10.1e\n\n\n", "Estimate of condition number", "",
1.0/rcond);
printf("%s\n%6s%10.1e\n\n",
"Estimate of error bound for computed solutions", "", errbnd);
}
else if (fail.code == NE_RCOND)
{
/* Matrix A is numerically singular.  Print estimate of */
/* reciprocal of condition number and solution */
printf("\n%s\n%6s%10.1e\n\n\n",
"Estimate of reciprocal of condition number", "", rcond);

/* nag_gen_real_mat_print (x04cac), see above. */
fflush(stdout);
nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
nrhs, b, pdb, "Solution", 0, &fail);
if (fail.code != NE_NOERROR)
{
printf("Error from nag_gen_real_mat_print (x04cac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
}
else if (fail.code == NE_POS_DEF)
{
/* The matrix A is not positive definite to working precision */
printf("%s%3ld%s\n\n", "The leading minor of order ",
fail.errnum, " is not positive definite");
}
else
{
printf("Error from "
"nag_real_sym_posdef_packed_lin_solve (f04bec).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
END:
NAG_FREE(ap);
NAG_FREE(b);

return exit_status;
}
```