/* nag_ode_ivp_rkts_onestep (d02pfc) Example Program. * * Copyright 2013 Numerical Algorithms Group. * * Mark 24, 2013. */ #include #include #include #include #ifdef __cplusplus extern "C" { #endif static void NAG_CALL f(double t, Integer n, const double *y, double *yp, Nag_Comm *comm); #ifdef __cplusplus } #endif #define N 2 int main(void) { /* Scalars */ double tol0 = 1.0e-3; Integer exit_status = 0; Integer liwsav, lrwsav, n; double hnext, hstart, tend, tgot, tol, tstart, waste; Integer fevals, i, j, k, stepcost, stepsok; /* Arrays */ static double ruser[1] = {-1.0}; double *rwsav = 0, *thresh = 0, *ygot = 0, *yinit = 0, *ypgot = 0; Integer *iwsav = 0; char nag_enum_arg[40]; /* NAG types */ NagError fail; Nag_RK_method method; Nag_ErrorAssess errass; Nag_Comm comm; INIT_FAIL(fail); printf("nag_ode_ivp_rkts_onestep (d02pfc) Example Program Results\n\n"); /* For communication with user-supplied functions: */ comm.user = ruser; n = N; liwsav = 130; lrwsav = 350 + 32 * n; if ( !(thresh = NAG_ALLOC(n, double)) || !(ygot = NAG_ALLOC(n, double)) || !(yinit = NAG_ALLOC(n, double)) || !(ypgot = NAG_ALLOC(n, double)) || !(iwsav = NAG_ALLOC(liwsav, Integer)) || !(rwsav = NAG_ALLOC(lrwsav, double)) ) { printf("Allocation failure\n"); exit_status = -1; goto END; } /* Skip heading in data file*/ scanf("%*[^\n] "); /* Set initial conditions for ODE and parameters for the integrator. */ scanf(" %39s%*[^\n] ", nag_enum_arg); /* nag_enum_name_to_value (x04nac) Converts NAG enum member name to value. */ method = (Nag_RK_method) nag_enum_name_to_value(nag_enum_arg); scanf(" %39s%*[^\n] ", nag_enum_arg); errass = (Nag_ErrorAssess) nag_enum_name_to_value(nag_enum_arg); scanf("%lf%lf%*[^\n] ", &tstart, &tend); for (j = 0; j < n; j++) scanf("%lf", &yinit[j]); scanf("%*[^\n] "); scanf("%lf%*[^\n] ", &hstart); for (j = 0; j < n; j++) scanf("%lf", &thresh[j]); scanf("%*[^\n] "); tol = tol0; for (i = 1; i <= 2; i++) { tol = tol * 0.1; /* Initialize Runge-Kutta method for integrating ODE using * nag_ode_ivp_rkts_setup (d02pqc). */ nag_ode_ivp_rkts_setup(n, tstart, tend, yinit, tol, thresh, method, errass, hstart, iwsav, rwsav, &fail); if (fail.code != NE_NOERROR) { printf("Error from nag_ode_ivp_rkts_setup (d02pqc).\n%s\n", fail.message); exit_status = 1; goto END; } printf(" Calculation with tol = %8.1e\n", tol); printf(" t y1 y2\n"); printf("%6.3f", tstart); for (k = 0; k < n; k++) printf(" %7.3f", yinit[k]); printf("\n"); tgot = tstart; while (tgot < tend) { /* Solve ODE by Runge-Kutta method by a sequence of single steps using * nag_ode_ivp_rkts_onestep (d02pfc). */ nag_ode_ivp_rkts_onestep(f, n, &tgot, ygot, ypgot, &comm, iwsav, rwsav, &fail); if (fail.code != NE_NOERROR) { printf("Error from nag_ode_ivp_rkts_onestep (d02pfc).\n%s\n", fail.message); exit_status = 2; goto END; } printf("%6.3f", tgot); for (k = 0; k < n; k++) printf(" %7.3f", ygot[k]); printf("\n"); } /* Get diagnostics on whole integration using * nag_ode_ivp_rkts_diag (d02ptc). */ nag_ode_ivp_rkts_diag(&fevals, &stepcost, &waste, &stepsok, &hnext, iwsav, rwsav, &fail); if (fail.code != NE_NOERROR) { printf("Error from nag_ode_ivp_rkts_diag (d02ptc).\n%s\n", fail.message); exit_status = 3; goto END; } printf("Cost of the integration in evaluations of f is %6ld\n\n", fevals); } END: NAG_FREE(thresh); NAG_FREE(yinit); NAG_FREE(ygot); NAG_FREE(ypgot); NAG_FREE(rwsav); NAG_FREE(iwsav); return exit_status; } static void NAG_CALL f(double t, Integer n, const double *y, double *yp, Nag_Comm *comm) { if (comm->user[0] == -1.0) { printf("(User-supplied callback f, first invocation.)\n"); comm->user[0] = 0.0; } yp[0] = y[1]; yp[1] = -y[0]; }