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QA5.FOR
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1985-11-29
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52 lines
C
C ..................................................................
C
C SUBROUTINE QA5
C
C PURPOSE
C TO COMPUTE INTEGRAL(EXP(-X)*FCT(X)/SQRT(X), SUMMED OVER X
C FROM 0 TO INFINITY).
C
C USAGE
C CALL QA5 (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 5-POINT GENERALIZED GAUSSIAN-
C LAGUERRE QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY,
C WHENEVER FCT(X) IS A POLYNOMIAL UP TO DEGREE 9.
C FOR REFERENCE, SEE
C CONCUS/CASSATT/JAEHNIG/MELBY, TABLES FOR THE EVALUATION OF
C INTEGRAL(X**BETA*EXP(-X)*F(X), SUMMED OVER X FROM 0 TO
C INFINITY) BY GAUSS-LAGUERRE QUADRATURE, MTAC, VOL.17,
C ISS.83 (1963), PP.245-256.
C
C ..................................................................
C
SUBROUTINE QA5(FCT,Y)
C
C
X=11.80719
Y=.1528087E-4*FCT(X)
X=6.414730
Y=Y+.002687291*FCT(X)
X=3.085937
Y=Y+.06774879*FCT(X)
X=1.074562
Y=Y+.4802772*FCT(X)
X=.1175813
Y=Y+1.221725*FCT(X)
RETURN
END