มีปัญหาเรื่อง error Index was outside the bounds of the array. ครับ

public void asianprice(double S,double K,double T,double r,double sigma,int NSimulations,int NStep)
    {
        double  dt, vsqrdt, drift;

        double str_S = S; //spot price
       double str_K = K; //strike
      double str_T = T; //maturity
       double str_r = r; //interest rate
       double str_sigma = sigma; //volatility
       double str_NSim = NSimulations; //no of monte carlo simulations
       double str_NSt = NStep; //no of time steps
        
        int i = 0, j;
        dt = T / (NStep - 1);
        vsqrdt = sigma * (Math.Pow(0.5, dt));
        drift = (r - (Math.Pow(2, sigma)) / 2) * dt;

        double[,] callpayoffvec = new double[i, 1];
        double[,] putpayoffvec = new double[i, 1];     
        int simtost = NSimulations * NStep;
        Random nsmlnsi = new Random();
        int randvec = nsmlnsi.Next(simtost);

        // find the result of sizeof of (S) and float 
        /*    for (i = 0; i < sizeof(int); i++)
            {
                Smat[i, 0] = S; // find the number of each S */

        for (i = 0; i <= NSimulations-1; i++)
        {
            double st = S;
            double curtime = 0;
            double tmpsum = 0;
            for (j = 0; j <= NStep-1; j++)
            {
                curtime = curtime + dt;
                st = st * Math.Exp(drift + vsqrdt + randvec);
                tmpsum = tmpsum + st;   
            }
            double AverageSVec = tmpsum / NStep;
           callpayoffvec[i, 1] = (Math.Max(AverageSVec - K, 0));
          putpayoffvec[i, 1] = (Math.Max(K - AverageSVec, 0));
        }
       double MC_callprice = Math.Exp(-r * T) * Mean(callpayoffvec);
       double MC_putprice = Math.Exp(-r * T) * Mean(putpayoffvec);

      
    }


    double Mean(double[,] dblArray)
    {
        double dblResult = 0;

        foreach (double dblValue in dblArray)
            dblResult += dblValue;
        return dblResult / dblArray.Length;
    }