/* nag_real_sym_posdef_tridiag_lin_solve (f04bgc) Example Program. * * Copyright 2004 Numerical Algorithms Group. * * Mark 8, 2004. */ #include #include #include #include #include int main(void) { /* Scalars */ double errbnd, rcond; Integer exit_status, i, j, n, nrhs, pdb; /* Arrays */ double *b, *d=0, *e=0; /* Nag Types */ NagError fail; Nag_OrderType order; #ifdef NAG_COLUMN_MAJOR #define B(I,J) b[(J-1)*pdb + I - 1] order = Nag_ColMajor; #else #define B(I,J) b[(I-1)*pdb + J - 1] order = Nag_RowMajor; #endif #define b_ref(a_1,a_2) b[(a_2)*8 + a_1 - 9] exit_status = 0; INIT_FAIL(fail); Vprintf("nag_real_sym_posdef_tridiag_lin_solve (f04bgc) Example Program" " Results\n\n"); /* Skip heading in data file */ Vscanf("%*[^\n] "); Vscanf("%ld%ld%*[^\n] ", &n, &nrhs); if (n>0 && nrhs>0) { /* Allocate memory */ if ( !(b = NAG_ALLOC(n*nrhs, double)) || !(d = NAG_ALLOC(n, double)) || !(e = NAG_ALLOC(n-1, double)) ) { Vprintf("Allocation failure\n"); exit_status = -1; goto END; } #ifdef NAG_COLUMN_MAJOR pdb = n; #else pdb = nrhs; #endif } else { Vprintf("%s\n", "n and/or nrhs too small"); exit_status = 1; return exit_status; } /* Read A from data file */ for (i = 1; i<=n; ++i) { Vscanf("%lf", &d[i-1]); } Vscanf("%*[^\n] "); for (i = 1;i<=n-1; ++i) { Vscanf("%lf", &e[i-1]); } Vscanf("%*[^\n] "); /* Read B from data file */ for (i=1; i<= n; ++i) { for (j=1; j<=nrhs; ++j) { Vscanf("%lf", &B(i,j)); } } Vscanf("%*[^\n] "); /* Solve the equations AX = B for X */ /* nag_real_sym_posdef_tridiag_lin_solve (f04bgc). * Computes the solution and error-bound to a real symmetric * positive-definite tridiagonal system of linear equations */ nag_real_sym_posdef_tridiag_lin_solve(order, n, nrhs, d, e, b, pdb, &rcond, &errbnd, &fail); if (fail.code == NE_NOERROR) { /* Print solution, estimate of condition number and approximate */ /* error bound */ /* nag_gen_real_mat_print (x04cac). * Print real general matrix (easy-to-use) */ nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n, nrhs, b, pdb, "Solution", 0, &fail); if (fail.code != NE_NOERROR) { Vprintf("Error from nag_gen_real_mat_print (x04cac).\n%s\n", fail.message); exit_status = 1; goto END; } Vprintf("\n%s\n%6s%9.1e\n", "Estimate of condition number", "", 1.0/rcond); Vprintf("\n\n"); Vprintf("%s\n%6s", "Estimate of error bound for computed solutions", ""); Vprintf("%9.1e\n\n", errbnd); } else if (fail.code == NE_RCOND) { /* Matrix A is numerically singular. Print estimate of */ /* reciprocal of condition number and solution */ Vprintf("\n"); Vprintf("%s\n%6s%9.1e\n", "Estimate of reciprocal of condition number", "", rcond); Vprintf("\n\n"); /* nag_gen_real_mat_print (x04cac), see above. */ nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n, nrhs, b, pdb, "Solution", 0, &fail); if (fail.code != NE_NOERROR) { Vprintf("Error from nag_gen_real_mat_print (x04cac).\n%s\n", fail.message); exit_status = 1; goto END; } } else if (fail.code == NE_POS_DEF) { Vprintf("%s%3ld%s\n\n", "The leading minor of order ", fail.errnum, " is not positive definite"); } END: if (b) NAG_FREE(b); if (d) NAG_FREE(d); if (e) NAG_FREE(e); return exit_status; }