## Gamma I FunctionMath Engineering Class

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

### Evaluate the incomplete Gamma function.

Examples:
```    GammaI(1.0, 1.0) = 0.632120558828558
GammaI(1.0, 2.0) = 0.864664716763387
GammaI(2.0, 1.0) = 0.264241117657115
GammaI(2.0, 2.0) = 0.593994150290162
GammaI(2.2, 1.1) = 0.271842079133223```
```    Gamma Function
GammaIC Function
GammaIT Function
GammaILn Function
GammaR Function
GammaCDF Function
GammaInverse Function
DGAMI 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 incomplete gamma function defined by

`    GammaI = integral from T = 0 to X of EXP(-T) * T^(A-1.0)`
GammaI 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 GammaI is very large or very small, because logarithmic variables are used. The function and both arguments are double precision.