private DoubleArray[] fdSenseCal(double[] xValues, double[] yValues, double[] xx)
{
int nData = yValues.Length;
double eps = 1e-6;
double scale = 0.5 / eps;
DoubleArray[] res = new DoubleArray[nData];
double[] temp = new double[nData];
PiecewisePolynomialResult pp;
for (int i = 0; i < nData; i++)
{
Array.Copy(yValues, 0, temp, 0, nData);
temp[i] += eps;
pp = PCHIP.interpolate(xValues, temp);
DoubleArray yUp = PPVAL.evaluate(pp, xx).row(0);
temp[i] -= 2 * eps;
pp = PCHIP.interpolate(xValues, temp);
DoubleArray yDown = PPVAL.evaluate(pp, xx).row(0);
res[i] = (DoubleArray)MA.scale(MA.subtract(yUp, yDown), scale);
}
return(res);
}