nag_ode_ivp_rkts_reset_tend (d02prc) resets the end point in an integration performed by
nag_ode_ivp_rkts_onestep (d02pfc).
nag_ode_ivp_rkts_reset_tend (d02prc) and its associated functions (
nag_ode_ivp_rkts_onestep (d02pfc),
nag_ode_ivp_rkts_setup (d02pqc),
nag_ode_ivp_rkts_interp (d02psc),
nag_ode_ivp_rkts_diag (d02ptc) and
nag_ode_ivp_rkts_errass (d02puc)) solve the initial value problem for a first-order system of ordinary differential equations. The functions, based on Runge–Kutta methods and derived from RKSUITE (see
Brankin et al. (1991)), integrate
where
is the vector of
solution components and
is the independent variable.
nag_ode_ivp_rkts_reset_tend (d02prc) is used to reset the final value of the independent variable,
, when the integration is already underway. It can be used to extend or reduce the range of integration. The new value must be beyond the current value of the independent variable (as returned in
tnow by
nag_ode_ivp_rkts_onestep (d02pfc)) in the current direction of integration. It is much more efficient to use nag_ode_ivp_rkts_reset_tend (d02prc) for this purpose than to use
nag_ode_ivp_rkts_setup (d02pqc) which involves the overhead of a complete restart of the integration.
If you want to change the direction of integration then you must restart by a call to
nag_ode_ivp_rkts_setup (d02pqc).
Brankin R W, Gladwell I and Shampine L F (1991) RKSUITE: A suite of Runge–Kutta codes for the initial value problems for ODEs SoftReport 91-S1 Southern Methodist University
Not applicable.
Not applicable.
None.
This example integrates a two body problem. The equations for the coordinates
of one body as functions of time
in a suitable frame of reference are
The initial conditions
lead to elliptic motion with
.
is selected and the system of ODEs is reposed as
over the range
. Relative error control is used with threshold values of
for each solution component and compute the solution at intervals of length
across the range using nag_ode_ivp_rkts_reset_tend (d02prc) to reset the end of the integration range. A high-order Runge–Kutta method (
) is also used with tolerances
and
in turn so that the solutions may be compared.