Proto

Generic Explicit RK4 Algorithm. More...
#include <Proto_RK4.H>
Generic Explicit RK4 Algorithm.
Given y'=f(y,t), it computes y_{t+1} from y_t using the following equations: k1=0.5*dt*f(y_t,t) k2=0.5*dt*f(y_t+k1,t+0.5*dt) k3=dt*f(y_t+k2,t+0.5*dt) k4=dt*f(y_t+k3,t+dt) y_{t+1}=y_t+k1/6+k2/3+k3/3+k4/6
This class is templated on three other classes X, dX, and F. These classes have the following requirements:
Container for y as well as any parameters that define the application. See EulerState in examples/Euler/src/EulerRK4.H for an example. Note that the Euler parameter gamma and the grid spacing dx are stored in this class. class X { Parameters and data };
Helper class to increment X at each intermediate step. It stores the current dX. See EulerDX in examples/Euler/src/EulerRK4.H for an example. class dX { public: Initialize the underlying dX data to a_State void init(X& a_State);
Performs the operation m_dX+=a_weight*a_incr, where m_dX is the underlying data void increment(double& a_weight,const dX& a_incr);
Performs the operation m_dX*=a_weight void operator*=(const double& a_weight); };
Helper class to compute f(y,t). This class doesn't contain any state. See EulerOp in examples/Euler/src/EulerRK4.H for an example. class F { public: Computes a_dt*f(a_State+a_DX,a_time) and puts the result in a_DX. NOTE it returns f scaled by dt void operator()(dX& a_DX, double a_time, double a_dt, X& a_State); };
WARNINGS: 1) There is no way to pass parameters or additional information to RK4. All of this information should be placed in the state class X. 2) F computes dt*f(y,t), so make sure to scale by dt.