RK4 Method

#include <stdio.h>
#include <math.h>

#define h 0.1 // "salto"

#define x0 1 // parâmetros iniciais
#define y0 2

#define N 100 // número de iterações

double f(double x, double y) // dy/dx = f(x,y)
{
    return 3*x*x*y; // função a ser resolvida
}

int main(void)
{
    int i;
    double K1, K2, K3, K4, x, y, yn;

    x=x0;
    y=y0;

    for (i=0; i<N; i++)
    {
        K1 = f(x,y);
        K2 = f(x+h/2,y+(h/2)*K1);
        K3 = f(x+h/2,y+(h/2)*K2);
        K4 = f(x+h,y+h*K3);

        yn = y + (h/6)*(K1 + 2*K2 + 2*K3 + K4);

        x+=h;

        printf("%lf\t%lf\n",yn,x);
    }

    return 0;
}