SLATEC Routines --- DGAMIC ---

*DECK DGAMIC
      DOUBLE PRECISION FUNCTION DGAMIC (A, X)
C***BEGIN PROLOGUE  DGAMIC
C***PURPOSE  Calculate the complementary incomplete Gamma function.
C***LIBRARY   SLATEC (FNLIB)
C***CATEGORY  C7E
C***TYPE      DOUBLE PRECISION (GAMIC-S, DGAMIC-D)
C***KEYWORDS  COMPLEMENTARY INCOMPLETE GAMMA FUNCTION, FNLIB,
C             SPECIAL FUNCTIONS
C***AUTHOR  Fullerton, W., (LANL)
C***DESCRIPTION
C
C   Evaluate the complementary incomplete Gamma function
C
C   DGAMIC = integral from X to infinity of EXP(-T) * T**(A-1.)  .
C
C   DGAMIC is evaluated for arbitrary real values of A and for non-
C   negative values of X (even though DGAMIC is defined for X .LT.
C   0.0), except that for X = 0 and A .LE. 0.0, DGAMIC is undefined.
C
C   DGAMIC, A, and X are DOUBLE PRECISION.
C
C   A slight deterioration of 2 or 3 digits accuracy will occur when
C   DGAMIC is very large or very small in absolute value, because log-
C   arithmic variables are used.  Also, if the parameter A is very close
C   to a negative INTEGER (but not a negative integer), there is a loss
C   of accuracy, which is reported if the result is less than half
C   machine precision.
C
C***REFERENCES  W. Gautschi, A computational procedure for incomplete
C                 gamma functions, ACM Transactions on Mathematical
C                 Software 5, 4 (December 1979), pp. 466-481.
C               W. Gautschi, Incomplete gamma functions, Algorithm 542,
C                 ACM Transactions on Mathematical Software 5, 4
C                 (December 1979), pp. 482-489.
C***ROUTINES CALLED  D1MACH, D9GMIC, D9GMIT, D9LGIC, D9LGIT, DLGAMS,
C                    DLNGAM, XERCLR, XERMSG
C***REVISION HISTORY  (YYMMDD)
C   770701  DATE WRITTEN
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   890531  REVISION DATE from Version 3.2
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900315  CALLs to XERROR changed to CALLs to XERMSG.  (THJ)
C   920528  DESCRIPTION and REFERENCES sections revised.  (WRB)
C***END PROLOGUE  DGAMIC