/// <summary>
/// Generates a 2d array of N stock paths over M time steps.
/// </summary>
/// <returns></returns>
public static double[,] GenerateMcPaths(int N, int M, double T, double r, double S0, double[] ssviParams)
{
Ssvi ssvi = new Ssvi(ssviParams);
// N = number of samples, M = number of time steps
double[,] pathOfS = new double[N, M];
double[] Z = new double[N];
double tau = T / M;
for (int m = 1; m < M; ++m) // foreach time step
{
Normal.Samples(Z, 0, 1); //Fill Z with normal 0,1 samples
double sqrtTau = Math.Sqrt(tau);
for (int n = 0; n < N; ++n) // foreach sample
{
pathOfS[n, 0] = S0;
double s_n_m = pathOfS[n, m - 1];
if (s_n_m < 0)
{
s_n_m = 1e-10;
}
double dw = sqrtTau * Z[n];
double k = Math.Log(s_n_m * Math.Exp(-r * T) / S0);
pathOfS[n, m] = s_n_m + r * s_n_m * tau + ssvi.VolatilityDup(tau * m, k) * s_n_m * dw;
}
}
return(pathOfS);
}
public static void RunVolatilityTest()
{
double alpha = Math.Sqrt(0.1);
double beta = 1;
double gamma = 0.7;
double eta = 0.2;
double rho = 0.3;
double r = 0.025;
double S = 100;
double K = 102.5313;
double T = 1;
double k = Math.Log(K * Math.Exp(-r * T) / S);
Ssvi SsviTest = new Ssvi(alpha, beta, gamma, eta, rho);
Console.WriteLine("SSVI Volatility = {0}", SsviTest.VolatilityDup(T, k));
}
public static double[][] ParallelGenerateMcPaths(int N, int M, double T, double r, double S0, double[] ssviParams)
{
Ssvi ssvi = new Ssvi(ssviParams);
// N = number of samples 10000, M = number of time steps 128
double[][] pathOfS = new double[N][];
double[] Z = new double[M];
double tau = T / M;
ConcurrentBag <double[]> paths = new ConcurrentBag <double[]>();
object mylock = new object();
Parallel.For(0, N, n =>
{
double[] vec = new double[M];
Normal.Samples(Z, 0, 1); //Fill Z with normal 0,1 samples
double sqrtTau = Math.Sqrt(tau);
for (int m = 0; m < (M - 1); ++m) // foreach sample
{
vec[0] = S0;
double s_n = vec[m];
if (s_n < 0)
{
s_n = 1e-10;
}
double dw = sqrtTau * Z[m];
double k = Math.Log(s_n * Math.Exp(-r * T) / S0);
vec[m + 1] = s_n + r * s_n * tau + ssvi.VolatilityDup(tau * m, k) * s_n * dw;
}
paths.Add(vec);
}
);
pathOfS = paths.ToArray();
return(pathOfS);
}
