/* nag_dspev (f08gac) Example Program. * * Copyright 2011 Numerical Algorithms Group. * * Mark 23, 2011. */ #include #include #include #include #include #include #include int main(void) { /* Scalars */ double eerrbd, eps; Integer exit_status = 0, i, j, n; /* Arrays */ char nag_enum_arg[40]; double *ap = 0, *dummy = 0, *w = 0; /* Nag Types */ Nag_OrderType order; Nag_UploType uplo; NagError fail; #ifdef NAG_COLUMN_MAJOR #define AP_UPPER(I, J) ap[J * (J - 1) / 2 + I - 1] #define AP_LOWER(I, J) ap[(2 * n - J) * (J - 1) / 2 + I - 1] order = Nag_ColMajor; #else #define AP_LOWER(I, J) ap[I * (I - 1) / 2 + J - 1] #define AP_UPPER(I, J) ap[(2 * n - I) * (I - 1) / 2 + J - 1] order = Nag_RowMajor; #endif INIT_FAIL(fail); printf("nag_dspev (f08gac) Example Program Results\n\n"); /* Skip heading in data file */ scanf("%*[^\n]"); scanf("%ld%*[^\n]", &n); /* Read uplo */ 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); /* Allocate memory */ if (!(ap = NAG_ALLOC(n*(n+1)/2, double)) || !(dummy = NAG_ALLOC(1, double)) || !(w = NAG_ALLOC(n, double))) { printf("Allocation failure\n"); exit_status = -1; goto END; } /* Read the upper or lower triangular part of the matrix A from data file */ if (uplo == Nag_Upper) { for (i = 1; i <= n; ++i) for (j = i; j <= n; ++j) scanf("%lf", &AP_UPPER(i, j)); scanf("%*[^\n]"); } else if (uplo == Nag_Lower) { for (i = 1; i <= n; ++i) for (j = 1; j <= i; ++j) scanf("%lf", &AP_LOWER(i, j)); scanf("%*[^\n]"); } /* nag_dspev (f08gac). * Solve the symmetric eigenvalue problem. */ nag_dspev(order, Nag_EigVals, uplo, n, ap, w, dummy, 1, &fail); if (fail.code != NE_NOERROR) { printf("Error from nag_dspev (f08gac).\n%s\n", fail.message); exit_status = 1; goto END; } /* Print solution */ printf("Eigenvalues\n"); for (j = 0; j < n; ++j) printf("%8.4f%s", w[j], (j+1)%8 == 0?"\n":" "); printf("\n"); /* Get the machine precision, eps, using nag_machine_precision (X02AJC) * and compute the approximate error bound for the computed eigenvalues. * Note that for the 2-norm, ||A|| = max {|w[i]|, i=0..n-1}, and since * the eigenvalues are in ascending order ||A|| = max( |w[0]|, |w[n-1]|). */ eps = nag_machine_precision; eerrbd = eps * MAX(fabs(w[0]), fabs(w[n-1])); /* Print the approximate error bound for the eigenvalues */ printf("\nError estimate for the eigenvalues\n"); printf("%11.1e\n", eerrbd); END: NAG_FREE(ap); NAG_FREE(dummy); NAG_FREE(w); return exit_status; } #undef AP_UPPER #undef AP_LOWER