This function evaluates the gamma probability density function.

Function Return Value

GAMPR — Function value, the value of the probability density function.   (Output)

Required Arguments

X — Argument for which the gamma probability density function is to be evaluated.   (Input)

A — The shape parameter of the gamma distribution.   (Input)
This parameter must be positive.

FORTRAN 90 Interface

Generic:                              GAMPR (X, A)

Specific:                             The specific interface names are S_GAMPR and D_GAMPR.

FORTRAN 77 Interface

Single:                                GAMPR (X, A)

Double:                              The double precision name is DGAMPR.

Description

The function GAMPR evaluates the gamma probability density function, defined as

Example

In this example, we evaluate the probability function at X = 4.0, A = 5.0.

 

      USE UMACH_INT
      USE GAMPR_INT
      IMPLICIT NONE

      INTEGER NOUT

      REAL X, A, PR

      CALL UMACH(2, NOUT)

      X = 4.0

      A = 5.0

      PR = GAMPR(X, A)

      WRITE (NOUT, 99999) X, A, PR

99999 FORMAT (' GAMPR(', F4.2, ', ', F4.2, ') = ', F6.4)

      END

Output

 

GAMPR(4.00, 5.00) = 0.1954

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