Digamma (Apache Commons Numbers Gamma 1.0 API)

java.lang.Object
- org.apache.commons.numbers.gamma.Digamma

```
public final class Digamma
extends Object
```
Digamma function.
It is defined as the logarithmic derivative of the $Γ$ (Gamma) function: $\frac{d}{d x} (\ln Γ (x)) = \frac{Γ^{'} (x)}{Γ (x)}$ .

See Also:

Gamma

- Method Summary
  
  All Methods Static Methods Concrete Methods
  Modifier and Type Method Description
  
  static double value(double x)
  Computes the digamma function.
  - Methods inherited from class java.lang.Object
    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Method Detail
  - value
```
public static double value(double x)
```
    Computes the digamma function. This is an independently written implementation of the algorithm described in Jose Bernardo, Algorithm AS 103: Psi (Digamma) Function, Applied Statistics, 1976. A reflection formula is incorporated to improve performance on negative values. Some of the constants have been changed to increase accuracy at the moderate expense of run-time. The result should be accurate to within 1e-8. relative tolerance for 0 < x < 1e-5 and within 1e-8 absolute tolerance otherwise.
    
    Parameters:
    
    x - Argument.
    
    Returns:
    
    digamma(x) to within 1e-8 relative or absolute error whichever is larger.