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DQA8.FOR
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1985-11-29
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61 lines
C
C ..................................................................
C
C SUBROUTINE DQA8
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 DQA8 (FCT,Y)
C PARAMETER FCT REQUIRES AN EXTERNAL STATEMENT
C
C DESCRIPTION OF PARAMETERS
C FCT - THE NAME OF AN EXTERNAL DOUBLE PRECISION FUNCTION
C SUBPROGRAM USED.
C Y - THE RESULTING DOUBLE PRECISION INTEGRAL VALUE.
C
C REMARKS
C NONE
C
C SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
C THE EXTERNAL DOUBLE PRECISION FUNCTION SUBPROGRAM FCT(X)
C MUST BE FURNISHED BY THE USER.
C
C METHOD
C EVALUATION IS DONE BY MEANS OF 8-POINT GENERALIZED GAUSS-
C LAGUERRE QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY
C WHENEVER FCT(X) IS A POLYNOMIAL UP TO DEGREE 15.
C FOR REFERENCE, SEE
C SHAO/CHEN/FRANK, TABLES OF ZEROS AND GAUSSIAN WEIGHTS OF
C CERTAIN ASSOCIATED LAGUERRE POLYNOMIALS AND THE RELATED
C GENERALIZED HERMITE POLYNOMIALS, IBM TECHNICAL REPORT
C TR00.1100 (MARCH 1964), PP.15-16.
C
C ..................................................................
C
SUBROUTINE DQA8(FCT,Y)
C
C
DOUBLE PRECISION X,Y,FCT
C
X=.21984272840962651D2
Y=.53096149480223645D-9*FCT(X)
X=.14972627088426393D2
Y=Y+.46419616897304213D-6*FCT(X)
X=.10093323675221343D2
Y=Y+.54237201850757630D-4*FCT(X)
X=.64831454286271704D1
Y=Y+.18645680172483611D-2*FCT(X)
X=.38094763614849071D1
Y=Y+.25760623071019947D-1*FCT(X)
X=.19051136350314284D1
Y=Y+.16762008279797166D0*FCT(X)
X=.67724908764928915D0
Y=Y+.56129491705706735D0*FCT(X)
X=.7479188259681827D-1
Y=Y+.10158589580332275D1*FCT(X)
RETURN
END