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QA6.FOR
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1985-11-29
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54 lines
C
C ..................................................................
C
C SUBROUTINE QA6
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 QA6 (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 6-POINT GENERALIZED GAUSSIAN-
C LAGUERRE QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY,
C WHENEVER FCT(X) IS A POLYNOMIAL UP TO DEGREE 11.
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 QA6(FCT,Y)
C
C
X=15.12996
Y=.5317103E-6*FCT(X)
X=9.124248
Y=Y+.0001714737*FCT(X)
X=5.196153
Y=Y+.007810781*FCT(X)
X=2.552590
Y=Y+.1032160*FCT(X)
X=.8983028
Y=Y+.5209846*FCT(X)
X=.09874701
Y=Y+1.140270*FCT(X)
RETURN
END