C
C     ..................................................................
C
C        SUBROUTINE QL4
C
C        PURPOSE
C           TO COMPUTE INTEGRAL(EXP(-X)*FCT(X), SUMMED OVER X FROM 0
C                               TO INFINITY).
C
C        USAGE
C           CALL QL4 (FCT,Y)
C           PARAMETER FCT REQUIRES AN EXTERNAL STATEMENT
C
C        DESCRIPTION OF PARAMETERS
C           FCT    - THE NAME OF AN EXTERNAL FUNCTION SUBPROGRAM USED.
C           Y      - THE RESULTING INTEGRAL VALUE.
C
C        REMARKS
C           NONE
C
C        SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
C           THE EXTERNAL FUNCTION SUBPROGRAM FCT(X) MUST BE FURNISHED
C           BY THE USER.
C
C        METHOD
C           EVALUATION IS DONE BY MEANS OF 4-POINT GAUSSIAN-LAGUERRE
C           QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY WHENEVER
C           FCT(X) IS A POLYNOMIAL UP TO DEGREE 7.
C           FOR REFERENCE, SEE
C           V.I.KRYLOV, APPROXIMATE CALCULATION OF INTEGRALS,
C           MACMILLAN, NEW YORK/LONDON, 1962, PP.130-132 AND 347-352.
C
C     ..................................................................
C
      SUBROUTINE QL4(FCT,Y)
C
C
      X=9.395071
      Y=.5392947E-3*FCT(X)
      X=4.536620
      Y=Y+.03888791*FCT(X)
      X=1.745761
      Y=Y+.3574187*FCT(X)
      X=.3225477
      Y=Y+.6031541*FCT(X)
      RETURN
      END
