ADAS Subroutine ingama

      function ingama(a,x)
	
C-----------------------------------------------------------------------
C
C    ****************** fortran77 function: ingama ****************** 
C
C  purpose: evaluates incomplete gamma function, P(a,x)
C
C  calling program: various
C
C  input : (r*8)  x      = function argument
C  input : (r*8)  a      = function argument
C
C  output: (r*8)  ingama = function name
C
C  author: Paul Bryans, University of Strathclyde
C
C  date:   20/02/04
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C  update: 
C
C-----------------------------------------------------------------------
      REAL*8              A,           X