/* nag_dgtcon (f07cgc) Example Program. * * Copyright 2004 Numerical Algorithms Group. * * Mark 23, 2011 * */ #include #include #include #include #include int main(void) { /* Scalars */ double anorm, rcond; 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_dgtcon (f07cgc) Example Program Results\n\n"); /* Skip heading in data file */ scanf("%*[^\n]"); scanf("%ld%*[^\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]"); /* Compute the 1-norm of A */ if (n == 1) { anorm = ABS(d[0]); } else { anorm = MAX(ABS(d[0])+ABS(dl[0]), ABS(d[n-1])+ABS(du[n-2])); for (i = 1; i < n-1; ++i) anorm = MAX(anorm, ABS(d[i])+ABS(dl[i])+ABS(du[i-1])); } /* Factorize the tridiagonal matrix A using nag_dgttrf (f07cdc). */ nag_dgttrf(n, dl, d, du, du2, ipiv, &fail); if (fail.code != NE_NOERROR) { printf("Error from nag_dgttrf (f07cdc).\n%s\n", fail.message); exit_status = 1; goto END; } /* Estimate the condition number of A using nag_dgtcon (f07cgc). */ nag_dgtcon(Nag_OneNorm, n, dl, d, du, du2, ipiv, anorm, &rcond, &fail); if (fail.code != NE_NOERROR) { printf("Error from nag_dgtcon (f07cgc).\n%s\n", fail.message); exit_status = 1; goto END; } /* Print the estimated condition number if A non-singular */ if (rcond >= nag_machine_precision) printf("Estimate of condition number = %11.2e\n\n", 1.0/rcond); else printf("A is singular to working precision. rcond = %11.2e\n\n", rcond); END: NAG_FREE(d); NAG_FREE(dl); NAG_FREE(du); NAG_FREE(du2); NAG_FREE(ipiv); return exit_status; }