// create and add to the chart data series representing Gaussian function
    //   y(x) = a * exp( -(x-b)*(x-b) / (2*c*c))
    // in the interval from x1 to x2
    void CreateGaussian(double x1, double x2, double a, double b, double c)
    {
      // number of points
      int cnt = 200;       var xvals = new double[cnt];
      var yvals = new double[cnt];

      double dx = (x2 - x1) / (cnt-1);

      for (int i = 0; i < cnt; i++)
      {
        var x = x1 + dx * i;
        xvals[i] = x;
        x =  (x - b) / c;
        yvals[i] = a * Math.Exp(-0.5*x*x);
      }

      var ds = new XYDataSeries()
      {
        XValuesSource = xvals,
        ValuesSource = yvals,
        ChartType = ChartType.Line
      };

      chart.Data.Children.Add(ds);
    }