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QA7.FOR
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1985-11-29
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56 lines
C
C ..................................................................
C
C SUBROUTINE QA7
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 QA7 (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 7-POINT GENERALIZED GAUSSIAN-
C LAGUERRE QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY,
C WHENEVER FCT(X) IS A POLYNOMIAL UP TO DEGREE 13.
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 QA7(FCT,Y)
C
C
X=18.52828
Y=.1725718E-7*FCT(X)
X=11.98999
Y=Y+.9432969E-5*FCT(X)
X=7.554091
Y=Y+.0007101852*FCT(X)
X=4.389793
Y=Y+.01570011*FCT(X)
X=2.180592
Y=Y+.1370111*FCT(X)
X=.7721379
Y=Y+.5462112*FCT(X)
X=.08511544
Y=Y+1.072812*FCT(X)
RETURN
END