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QA9.FOR
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1985-11-29
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2KB
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C
C ..................................................................
C
C SUBROUTINE QA9
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 QA9 (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 9-POINT GENERALIZED GAUSSIAN-
C LAGUERRE QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY,
C WHENEVER FCT(X) IS A POLYNOMIAL UP TO DEGREE 17.
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 QA9(FCT,Y)
C
C
X=25.48598
Y=.1565640E-10*FCT(X)
X=18.04651
Y=Y+.2093441E-7*FCT(X)
X=12.77183
Y=Y+.3621309E-5*FCT(X)
X=8.769757
Y=Y+.0001836225*FCT(X)
X=5.694423
Y=Y+.003777045*FCT(X)
X=3.369176
Y=Y+.03728008*FCT(X)
X=1.692395
Y=Y+.1946035*FCT(X)
X=.6032364
Y=Y+.5696146*FCT(X)
X=.06670223
Y=Y+.9669914*FCT(X)
RETURN
END