## Gamma I Ln FunctionMath Engineering Class

```Public Function GammaILn( _
ByVal vA As Variant _
, ByVal vX As Variant _
) As Variant```

### Evaluate the log of the incomplete Gamma function.

Examples:
```    GammaILn(1.0, 1.0) = -0.458675145387082
GammaILn(1.0, 2.0) = -0.145413457868859
GammaILn(2.0, 1.0) = -1.33089326820405
GammaILn(2.0, 2.0) = -0.520885807664344
GammaILn(2.2, 1.1) = -1.30253397271658
GammaILn(2.2, 1.1) = Log(GammaI(2.2, 1.1))```
```    GammaLn Function
GammaI Function
Gamma Function
DLNGMI Function```
vA: Function returns Null if vA is Null or cannot be fixed up to a Double precision floating point number.
vX: Function returns Null if vX is Null or cannot be fixed up to a Double precision floating point number.

Evaluate the log of the incomplete gamma function defined by

`    GammaILn = log of integral from T = 0 to X of EXP(-T) * T^(A-1.0)`
GammaILn is evaluated for positive values of A and non-negative values of X. A slight deterioration of 2 or 3 digits accuracy will occur when GammaILn is very large or very small, because logarithmic variables are used. The function and both arguments are double precision.