Double psi(Int32 derivate, Double x)
Returns the polygamma function psi^((m))(x) of order derivate.
| # | Name | Description |
|---|---|---|
| 1 | derivate | order m of the polygamma function |
| 2 | only 0 and 1 are supported. | |
| 3 | x | argument |
| 4 | real positive. |
Returns: Double
Remarks:
Computes the m-th derivative of the logarithm of the Gamma function:
psi^((m))(x) = (d^(m+1))/(dx^(m+1))lnGamma(x) .
Defined behavior: if derivate is 0 the function returns psi(x) (see Dew.Math.Units.Probabilities.digamma); if derivate is 1 it returns psi^((1))(x) (see Dew.Math.Units.Probabilities.trigamma). Both return NAN for x <= 0. Any other value of derivate is not supported and raises an EMtxVecException.