/* nag_lapacklin_dgttrf (f07cdc) Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
*
* Mark 27.0, 2019.
*/

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

int main(void)
{
/* Scalars */
Integer exit_status = 0, i, n;

/* Arrays */
double *d = 0, *dl = 0, *du = 0, *du2 = 0;
Integer *ipiv = 0;

/* Nag Types */
NagError fail;

INIT_FAIL(fail);

printf("nag_lapacklin_dgttrf (f07cdc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%*[^\n]", &n);
if (n < 0) {
printf("Invalid n\n");
exit_status = 1;
goto END;
}
/* Allocate memory */
if (!(d = NAG_ALLOC(n, double)) ||
!(dl = NAG_ALLOC(n - 1, double)) ||
!(du = NAG_ALLOC(n - 1, double)) ||
!(du2 = NAG_ALLOC(n - 2, double)) || !(ipiv = NAG_ALLOC(n, Integer)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* Read the tridiagonal matrix A from data file */
for (i = 0; i < n - 1; ++i)
scanf("%lf", &du[i]);
scanf("%*[^\n]");
for (i = 0; i < n; ++i)
scanf("%lf", &d[i]);
scanf("%*[^\n]");
for (i = 0; i < n - 1; ++i)
scanf("%lf", &dl[i]);
scanf("%*[^\n]");

/* Factorize the tridiagonal matrix A using nag_lapacklin_dgttrf (f07cdc). */
nag_lapacklin_dgttrf(n, dl, d, du, du2, ipiv, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_dgttrf (f07cdc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Print details of the factorization */
printf("Details of factorization\n\n");
printf(" Second superdiagonal of U\n");
for (i = 0; i < n - 2; ++i)
printf("%9.4f%s", du2[i], i % 8 == 7 ? "\n" : " ");
printf("\n\n First superdiagonal of U\n");
for (i = 0; i < n - 1; ++i)
printf("%9.4f%s", du[i], i % 8 == 7 ? "\n" : " ");
printf("\n\n Main diagonal of U\n");
for (i = 0; i < n; ++i)
printf("%9.4f%s", d[i], i % 8 == 7 ? "\n" : " ");

printf("\n\n Multipliers\n");
for (i = 0; i < n - 1; ++i)
printf("%9.4f%s", dl[i], i % 8 == 7 ? "\n" : " ");
printf("\n\n Vector of interchanges\n");
for (i = 0; i < n; ++i)
printf("%9" NAG_IFMT "%s", ipiv[i], i % 5 == 4 ? "\n" : " ");
printf("\n");
END:
NAG_FREE(d);
NAG_FREE(dl);
NAG_FREE(du);
NAG_FREE(du2);
NAG_FREE(ipiv);
return exit_status;
}