/* nag_lapackeig_dsyevx (f08fbc) Example Program.
*
* Copyright 2024 Numerical Algorithms Group.
*
* Mark 30.1, 2024.
*/
#include <nag.h>
#include <stdio.h>
int main(void) {
/* Scalars */
double abstol, vl, vu;
Integer i, il = 0, iu = 0, j, m, n, pda, pdz;
Integer exit_status = 0;
/* Arrays */
char nag_enum_arg[40];
double *a = 0, *w = 0, *z = 0;
Integer *index = 0;
/* Nag Types */
Nag_OrderType order;
Nag_RangeType range;
Nag_UploType uplo;
Nag_JobType job;
NagError fail, fail_print;
#ifdef NAG_COLUMN_MAJOR
#define A(I, J) a[(J - 1) * pda + I - 1]
#define Z(I, J) z[(J - 1) * pdz + I - 1]
order = Nag_ColMajor;
#else
#define A(I, J) a[(I - 1) * pda + J - 1]
#define Z(I, J) z[(I - 1) * pdz + J - 1]
order = Nag_RowMajor;
#endif
INIT_FAIL(fail);
printf("nag_lapackeig_dsyevx (f08fbc) Example Program Results\n\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%*[^\n]", &n);
/* Read uplo, range and job */
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);
scanf("%39s%*[^\n]", nag_enum_arg);
range = (Nag_RangeType)nag_enum_name_to_value(nag_enum_arg);
scanf("%39s%*[^\n]", nag_enum_arg);
job = (Nag_JobType)nag_enum_name_to_value(nag_enum_arg);
/* Allocate memory */
if (!(a = NAG_ALLOC(n * n, double)) || !(w = NAG_ALLOC(n, double)) ||
!(z = NAG_ALLOC(n * n, double)) || !(index = NAG_ALLOC(n, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
pda = n;
pdz = n;
/* Read the lower and upper bounds of the interval to be searched,
* and read the upper triangular part of the matrix A from data file
*/
scanf("%lf%lf%*[^\n]", &vl, &vu);
for (i = 1; i <= n; ++i)
for (j = i; j <= n; ++j)
scanf("%lf", &A(i, j));
scanf("%*[^\n]");
/* Set the absolute error tolerance for eigenvalues. With abstol
* set to zero, the default value is used instead.
*/
abstol = 0.0;
/* nag_lapackeig_dsyevx (f08fbc).
* Solve the symmetric eigenvalue problem.
*/
nag_lapackeig_dsyevx(order, job, range, uplo, n, a, pda, vl, vu, il, iu,
abstol, &m, w, z, pdz, index, &fail);
if (fail.code != NE_NOERROR && fail.code != NE_CONVERGENCE) {
printf("Error from nag_lapackeig_dsyevx (f08fbc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Normalize the eigenvectors */
for (j = 1; j <= m; j++)
for (i = n; i >= 1; i--)
Z(i, j) = Z(i, j) / Z(1, j);
/* Print solution */
printf("Number of eigenvalues found =%5" NAG_IFMT "\n", m);
printf("\nEigenvalues\n");
for (j = 0; j < m; ++j)
printf("%8.4f%s", w[j], (j + 1) % 8 == 0 ? "\n" : " ");
printf("\n\n");
/* nag_file_print_matrix_real_gen (x04cac).
* Print selected eigenvectors.
*/
INIT_FAIL(fail_print);
fflush(stdout);
nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
m, z, pdz, "Selected eigenvectors", 0,
&fail_print);
if (fail_print.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_gen (x04cac).\n%s\n",
fail_print.message);
exit_status = 1;
goto END;
}
if (fail.code == NE_CONVERGENCE) {
printf("eigenvectors failed to converge\n");
printf("Indices of eigenvectors that did not converge\n");
for (j = 0; j < m; ++j)
printf("%8" NAG_IFMT "%s", index[j], (j + 1) % 8 == 0 ? "\n" : " ");
}
END:
NAG_FREE(a);
NAG_FREE(w);
NAG_FREE(z);
NAG_FREE(index);
return exit_status;
}
#undef A
#undef Z