rung-kutta
・Runge-Kutta法
微分方程式が
dx/dt ＝ -x + tsin(t)
のとき
/* Differential Equation : F(t,x) */
double f(double t,double x){
double y;
y = -x + t*sin(t);
return y;
}
————————————————————————————————
/* Runge-Kutta Function */
double runge_kutta(double x0){ // x0：Initial Value
double h = 0.01; // Step Size
double k1,k2,k3,k4,x,nx,T;
// Initial Value
x = x0;
// Runge-Kutta Method
for(T = 0.0;T < 50;T += h){
k1 = f(T,x);
k2 = f(T+h/2,x+(h/2)*k1);
k3 = f(T+h/2,x+(h/2)*k2);
k4 = f(T+h,x+h*k3);
nx = x + h*(k1+2*k2+2*k3+k4)/6;
x = nx;
}
return x;
}
