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DQH8.FOR
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1985-11-29
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57 lines
C
C ..................................................................
C
C SUBROUTINE DQH8
C
C PURPOSE
C TO COMPUTE INTEGRAL(EXP(-X*X)*FCT(X), SUMMED OVER X FROM
C -INFINITY TO +INFINITY).
C
C USAGE
C CALL DQH8 (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-HERMITE
C QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY WHENEVER
C 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.213-214.
C
C ..................................................................
C
SUBROUTINE DQH8(FCT,Y)
C
C
DOUBLE PRECISION X,Y,Z,FCT
C
X=.29306374202572440D1
Z=-X
Y=.19960407221136762D-3*(FCT(X)+FCT(Z))
X=.19816567566958429D1
Z=-X
Y=Y+.17077983007413475D-1*(FCT(X)+FCT(Z))
X=.11571937124467802D1
Z=-X
Y=Y+.20780232581489188D0*(FCT(X)+FCT(Z))
X=.38118699020732212D0
Z=-X
Y=Y+.66114701255824129D0*(FCT(X)+FCT(Z))
RETURN
END