FUNCTION GAMMP(A,X)
      IMPLICIT DOUBLE PRECISION (A-H,O-Z)
      IF(X.LT.0..OR.A.LE.0.)PAUSE
      IF(X.LT.A+1.)THEN
        CALL GSER(GAMMP,A,X,GLN)
      ELSE
        CALL GCF(GAMMCF,A,X,GLN)
        GAMMP=1.-GAMMCF
      ENDIF
      RETURN
      END