/* nag_lapackeig_zheevr (f08frc) Example Program.
*
* Copyright 2024 Numerical Algorithms Group.
*
* Mark 30.1, 2024.
*/
#include <nag.h>
#include <stdio.h>
int main(void) {
/* Scalars */
double abstol, vl = 0.0, vu = 0.0;
Integer i, il, iu, j, m, n, pda, pdz;
Integer exit_status = 0;
/* Arrays */
Complex *a = 0, *z = 0;
double *w = 0;
Integer *isuppz = 0;
/* Nag Types */
Nag_OrderType order;
NagError fail;
#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_zheevr (f08frc) Example Program Results\n\n");
/* Skip heading in data file and read n and the lower and upper
* indices of the smallest and largest eigenvalues to be found.
*/
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%*[^\n]", &n, &il, &iu);
m = iu - il + 1;
pda = n;
pdz = n;
/* Allocate memory */
if (!(a = NAG_ALLOC(n * n, Complex)) || !(z = NAG_ALLOC(n * pdz, Complex)) ||
!(w = NAG_ALLOC(n, double)) || !(isuppz = NAG_ALLOC(2 * pdz, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
/* Read the upper triangular part of the matrix A from data file */
for (i = 1; i <= n; ++i)
for (j = i; j <= n; ++j)
scanf(" ( %lf , %lf )", &A(i, j).re, &A(i, j).im);
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_zheevr (f08frc).
* Solve the symmetric eigenvalue problem.
*/
nag_lapackeig_zheevr(order, Nag_DoBoth, Nag_Indices, Nag_Upper, n, a, pda, vl,
vu, il, iu, abstol, &m, w, z, pdz, isuppz, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapackeig_zheevr (f08frc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* nag_complex_divide (a02cdc).
* Normalize the eigenvectors.
*/
for (j = 1; j <= m; j++)
for (i = n; i >= 1; i--)
Z(i, j) = nag_complex_divide(Z(i, j), Z(1, j));
/* Print solution */
printf("Selected eigenvalues\n");
for (j = 0; j < m; ++j)
printf("%8.4f%s", w[j], (j + 1) % 8 == 0 ? "\n" : " ");
printf("\n");
/* nag_file_print_matrix_complex_gen (x04dac).
* Print selected eigenvectors.
*/
fflush(stdout);
nag_file_print_matrix_complex_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag,
n, m, z, pdz, "Selected eigenvectors", 0,
&fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_complex_gen (x04dac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
END:
NAG_FREE(a);
NAG_FREE(z);
NAG_FREE(w);
NAG_FREE(isuppz);
return exit_status;
}
#undef A
#undef Z