using System;
public static partial class ode{

public static (vector,vector) rkstep23(
	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;
        return (yh,er);
}//rkstep23

}//class