void TEpidemModel::RungeKutta(const TFltV& y, const TFltV& dydx, double x, double h, TFltV& SirOutV) {
const int n = y.Len();
IAssert(y.Len() == n && dydx.Len() == n);
TFltV dym(n), dyt(n), yt(n);
int i;
double hh=h*0.5;
double h6=h/6.0;
double xh=x+hh;
for (i=0; i < n; i++) {
yt[i]=y[i]+hh*dydx[i];
}
GetDerivs(xh, yt, dyt);
for (i=0; i<n; i++) {
yt[i]=y[i]+hh*dyt[i];
}
GetDerivs(xh,yt,dym);
for (i=0; i<n; i++) {
yt[i]=y[i]+h*dym[i];
dym[i] += dyt[i];
}
GetDerivs(x+h,yt,dyt);
SirOutV.Clr(false);
for (i=0; i<n; i++) {
SirOutV.Add(y[i]+h6 * (dydx[i]+dyt[i]+2.0*dym[i]));
}
}
OpenANN::Environment::State DoublePoleBalancing::rk4(const State& s, double force, const State& der)
{
const double TIME_DELTA = 0.01;
State result(6);
double hh = TIME_DELTA * 0.5, h6 = TIME_DELTA / 6.0;
State dym(6);
State dyt(6);
State yt(6);
yt = s + hh * der;
dyt = derivative(yt, force);
dyt(0) = yt(1);
dyt(2) = yt(3);
dyt(4) = yt(5);
yt = s + hh * dyt;
dym = derivative(yt, force);
dym(0) = yt(1);
dym(2) = yt(3);
dym(4) = yt(5);
yt = s + TIME_DELTA * dym;
dym += dyt;
dyt = derivative(yt, force);
dyt(0) = yt(1);
dyt(2) = yt(3);
dyt(4) = yt(5);
result = s + h6 * (der + dyt + 2.0 * dym);
return result;
}
