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DQL8.FOR
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1985-11-29
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61 lines
C
C ..................................................................
C
C SUBROUTINE DQL8
C
C PURPOSE
C TO COMPUTE INTEGRAL(EXP(-X)*FCT(X), SUMMED OVER X
C FROM 0 TO INFINITY).
C
C USAGE
C CALL DQL8 (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 GAUSSIAN-LAGUERRE
C 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.24-25.
C
C ..................................................................
C
SUBROUTINE DQL8(FCT,Y)
C
C
DOUBLE PRECISION X,Y,FCT
C
X=.22863131736889264D2
Y=.10480011748715104D-8*FCT(X)
X=.15740678641278005D2
Y=Y+.8485746716272532D-6*FCT(X)
X=.10758516010180995D2
Y=Y+.9076508773358213D-4*FCT(X)
X=.70459054023934657D1
Y=Y+.27945362352256725D-2*FCT(X)
X=.42667001702876588D1
Y=Y+.33343492261215652D-1*FCT(X)
X=.22510866298661307D1
Y=Y+.17579498663717181D0*FCT(X)
X=.9037017767993799D0
Y=Y+.41878678081434296D0*FCT(X)
X=.17027963230510100D0
Y=Y+.36918858934163753D0*FCT(X)
RETURN
END