C QG4 10
C ..................................................................QG4 20
C QG4 30
C SUBROUTINE QG4 QG4 40
C QG4 50
C PURPOSE QG4 60
C TO COMPUTE INTEGRAL(FCT(X), SUMMED OVER X FROM XL TO XU) QG4 70
C QG4 80
C USAGE QG4 90
C CALL QG4 (XL,XU,FCT,Y) QG4 100
C PARAMETER FCT REQUIRES AN EXTERNAL STATEMENT QG4 110
C QG4 120
C DESCRIPTION OF PARAMETERS QG4 130
C XL - THE LOWER BOUND OF THE INTERVAL. QG4 140
C XU - THE UPPER BOUND OF THE INTERVAL. QG4 150
C FCT - THE NAME OF AN EXTERNAL FUNCTION SUBPROGRAM USED. QG4 160
C Y - THE RESULTING INTEGRAL VALUE. QG4 170
C QG4 180
C REMARKS QG4 190
C NONE QG4 200
C QG4 210
C SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED QG4 220
C THE EXTERNAL FUNCTION SUBPROGRAM FCT(X) MUST BE FURNISHED QG4 230
C BY THE USER. QG4 240
C QG4 250
C METHOD QG4 260
C EVALUATION IS DONE BY MEANS OF 4-POINT GAUSS QUADRATURE QG4 270
C FORMULA, WHICH INTEGRATES POLYNOMIALS UP TO DEGREE 7 QG4 280
C EXACTLY. QG4 290
C FOR REFERENCE, SEE QG4 300
C V.I.KRYLOV, APPROXIMATE CALCULATION OF INTEGRALS, QG4 310
C MACMILLAN, NEW YORK/LONDON, 1962, PP.100-111 AND 337-338. QG4 320
C QG4 330
C ..................................................................QG4 340
C QG4 350
SUBROUTINE QG4(XL,XU,FCT,Y) QG4 360
C QG4 370
C QG4 380
A=.5*(XU+XL) QG4 390
B=XU-XL QG4 400
C=.4305682*B QG4 410
Y=.1739274*(FCT(A+C)+FCT(A-C)) QG4 420
C=.1699905*B QG4 430
Y=B*(Y+.3260726*(FCT(A+C)+FCT(A-C))) QG4 440
RETURN QG4 450
END QG4 460