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QA3.FOR
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1985-11-29
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48 lines
C
C ..................................................................
C
C SUBROUTINE QA3
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 QA3 (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 3-POINT GENERALIZED GAUSSIAN-
C LAGUERRE QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY,
C WHENEVER FCT(X) IS A POLYNOMIAL UP TO DEGREE 5.
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 QA3(FCT,Y)
C
C
X=5.525344
Y=.009060020*FCT(X)
X=1.784493
Y=Y+.3141346*FCT(X)
X=.1901635
Y=Y+1.449259*FCT(X)
RETURN
END