```/* nag_lapackeig_dsyevr (f08fdc) Example Program.
*
* Copyright 2020 Numerical Algorithms Group.
*
* Mark 27.1, 2020.
*/

#include <nag.h>
#include <stdio.h>

int main(void) {
/* Scalars */
double abstol, vl = 0.0, vu = 0.0;
Integer exit_status = 0, i, il, iu, j, m, n;
Integer pda, pdz;
/* Arrays */
double *a = 0, *w = 0, *z = 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_dsyevr (f08fdc) 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;
/* Allocate memory */
if (!(a = NAG_ALLOC(n * n, double)) || !(w = NAG_ALLOC(n, double)) ||
!(z = NAG_ALLOC(n * n, double)) ||
!(isuppz = NAG_ALLOC(m * 2, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

pda = n;
pdz = n;

/* 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", &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_dsyevr (f08fdc).
* Solve the symmetric eigenvalue problem.
*/
nag_lapackeig_dsyevr(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_dsyevr (f08fdc).\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("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_real_gen (x04cac).
* Print selected eigenvectors.
*/
fflush(stdout);
nag_file_print_matrix_real_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_real_gen (x04cac).\n%s\n",
fail.message);
exit_status = 1;
}

END:
NAG_FREE(a);
NAG_FREE(w);
NAG_FREE(z);
NAG_FREE(isuppz);

return exit_status;
}

#undef A
#undef Z
```