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SUBROUTINE QA4

PURPOSE
   TO COMPUTE INTEGRAL(EXP(-X)*FCT(X)/SQRT(X), SUMMED OVER X
		       FROM 0 TO INFINITY).

USAGE
   CALL QA4 (FCT,Y)
   PARAMETER FCT REQUIRES AN EXTERNAL STATEMENT

DESCRIPTION OF PARAMETERS
   FCT	  - THE NAME OF AN EXTERNAL FUNCTION SUBPROGRAM USED.
   Y	  - THE RESULTING INTEGRAL VALUE.

REMARKS
   NONE

SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
   THE EXTERNAL FUNCTION SUBPROGRAM FCT(X) MUST BE FURNISHED
   BY THE USER.

METHOD
   EVALUATION IS DONE BY MEANS OF 4-POINT GENERALIZED GAUSSIAN-
   LAGUERRE QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY,
   WHENEVER FCT(X) IS A POLYNOMIAL UP TO DEGREE 7.
   FOR REFERENCE, SEE
   CONCUS/CASSATT/JAEHNIG/MELBY, TABLES FOR THE EVALUATION OF
   INTEGRAL(X**BETA*EXP(-X)*F(X), SUMMED OVER X FROM 0 TO
   INFINITY) BY GAUSS-LAGUERRE QUADRATURE, MTAC, VOL.17,
   ISS.83 (1963), PP.245-256.