public partial class ode{

public static vector[]
rkstep23(System.Func<double,vector,vector> F, double x, vector y, double h)
{// Embedded Runge-Kutta stepper of the order 2-3
	vector k0 = F(x,y);
	vector k1 = F(x+h/2  , y+(h/2  )*k0);
	vector k2 = F(x+3*h/4, y+(3*h/4)*k1);
	vector ka = (2*k0+3*k1+4*k2)/9;
	vector kb = k1;
	vector yh = y+ka*h;
	vector er = (ka-kb)*h;
	vector[] result={yh,er};
	return result;
}//rkstep23

}//class