public void RK2Test()
{
Func <double, double, double> ode = (t, y) => t + 2 * y * t;
Func <double, double> sol = (t) => 0.5 * (Math.Exp(t * t) - 1);
double ratio = double.NaN;
double error = 0;
double oldError = 0;
for (int k = 0; k < 4; k++)
{
double y0 = 0;
double[] y_t = RungeKutta.SecondOrder(y0, 0, 2, Convert.ToInt32(Math.Pow(2, k + 6)), ode);
error = Math.Abs(sol(2) - y_t.Last());
if (oldError != 0)
{
ratio = Math.Log(oldError / error, 2);
}
oldError = error;
Console.WriteLine(string.Format("{0}, {1}", error, ratio));
}
Assert.AreEqual(2, ratio, 0.01);// Check error convergence order
}
/// <summary>
/// Método Runge Kutta de Segunda ordem para equações diferenciais
/// </summary>
/// <param name="y0">Valor Inicial</param>
/// <param name="start">Tempo Inicial</param>
/// <param name="end">Tempo Final</param>
/// <param name="dydx">Equação diferencial a ser calculada</param>
/// <returns></returns>
public double RungeKutta2(double y0, double start, double end, Func <double, double, double> dydx)
{
return(RungeKutta.SecondOrder(y0, start, end, 10, dydx)[9]);
}