Returns the \psi _1 function, also known as the trigamma function.

Namespace: Imsl.Math
Assembly: ImslCS (in ImslCS.dll) Version: 6.5.0.0

Syntax

C#
public static double Psi1(
	double x
)
Visual Basic (Declaration)
Public Shared Function Psi1 ( _
	x As Double _
) As Double
Visual C++
public:
static double Psi1(
	double x
)

Parameters

x
Type: System..::.Double
A double value, the point at which the trigamma function is to be evaluated.

Return Value

A double value specifying the trigamma function of x. If x is a negative integer or zero, the result is NaN.

Remarks

The trigamma function, \psi _1 (x), is defined to be

\psi _1\left(x\right)=\frac{d^2}{dx^2}\ln \Gamma(x)

The trigamma function is not defined for integers less than or equal to zero.

See Also