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# Gamma Upper Reg

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The regularized upper incomplete Gamma integral
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## GammaUpper Reg

 doublegammaUpper_reg( double a double x )
This function returns the regularized "upper" incomplete Gamma Integral. Regularization is equivalent to normalisation, ensuring the result always lies between 0 and 1. Thus

When x < 1 or x < a the solution is calculated using 1 - Maths/Special/Gamma/Gamma_Lower_Reg .

## Accuracy

Tested at random a, x. <pre> Relative error: domain(a,x) domain # trials peak rms 0.5,100 0,100 200000 1.9e-14 1.7e-15 0.01,0.5 0,100 200000 1.4e-13 1.6e-15 </pre>

### Note

In this implementation both arguments must be positive. The integral is evaluated by either a power series or continued fraction expansion, depending on the relative values of a and x.

## Example:

#include <stdio.h>
#include <codecogs/maths/special/gamma/gamma_upper_reg.h>
void main
{
for(double a=0; a<3; a+=0.25)
{
double y=Maths::Special::Gamma::gammaUpper_reg(a, 2);
printf("\n gammaUpper_reg(%lf, 2)=%lf", a,y);
}
}

## Output:

gammaUpper_reg(0.000000, 2)=0.000000
gammaUpper_reg(0.250000, 2)=0.017286
gammaUpper_reg(0.500000, 2)=0.045500
gammaUpper_reg(0.750000, 2)=0.085056
gammaUpper_reg(1.000000, 2)=0.135335
gammaUpper_reg(1.250000, 2)=0.194847
gammaUpper_reg(1.500000, 2)=0.261464
gammaUpper_reg(1.750000, 2)=0.332706
gammaUpper_reg(2.000000, 2)=0.406006
gammaUpper_reg(2.250000, 2)=0.478944
gammaUpper_reg(2.500000, 2)=0.549416
gammaUpper_reg(2.750000, 2)=0.615734

## References:

Cephes Math Library Release 2.8: June, 2000

### Parameters

 a argument. Must be positive. x lower, positive, limit of the integral.

### Authors

Stephen L.Moshier. Copyright 1984, 1987, 1989, 1992, 2000
Updated by Will Bateman
##### Source Code

Source code is available when you agree to a GP Licence or buy a Commercial Licence.

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