C QG3 10
C ..................................................................QG3 20
C QG3 30
C SUBROUTINE QG3 QG3 40
C QG3 50
C PURPOSE QG3 60
C TO COMPUTE INTEGRAL(FCT(X), SUMMED OVER X FROM XL TO XU) QG3 70
C QG3 80
C USAGE QG3 90
C CALL QG3 (XL,XU,FCT,Y) QG3 100
C PARAMETER FCT REQUIRES AN EXTERNAL STATEMENT QG3 110
C QG3 120
C DESCRIPTION OF PARAMETERS QG3 130
C XL - THE LOWER BOUND OF THE INTERVAL. QG3 140
C XU - THE UPPER BOUND OF THE INTERVAL. QG3 150
C FCT - THE NAME OF AN EXTERNAL FUNCTION SUBPROGRAM USED. QG3 160
C Y - THE RESULTING INTEGRAL VALUE. QG3 170
C QG3 180
C REMARKS QG3 190
C NONE QG3 200
C QG3 210
C SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED QG3 220
C THE EXTERNAL FUNCTION SUBPROGRAM FCT(X) MUST BE FURNISHED QG3 230
C BY THE USER. QG3 240
C QG3 250
C METHOD QG3 260
C EVALUATION IS DONE BY MEANS OF 3-POINT GAUSS QUADRATURE QG3 270
C FORMULA, WHICH INTEGRATES POLYNOMIALS UP TO DEGREE 5 QG3 280
C EXACTLY. QG3 290
C FOR REFERENCE, SEE QG3 300
C V.I.KRYLOV, APPROXIMATE CALCULATION OF INTEGRALS, QG3 310
C MACMILLAN, NEW YORK/LONDON, 1962, PP.100-111 AND 337-338. QG3 320
C QG3 330
C ..................................................................QG3 340
C QG3 350
SUBROUTINE QG3(XL,XU,FCT,Y) QG3 360
C QG3 370
C QG3 380
A=.5*(XU+XL) QG3 390
B=XU-XL QG3 400
Y=.3872983*B QG3 410
Y=.2777778*(FCT(A+Y)+FCT(A-Y)) QG3 420
Y=B*(Y+.4444444*FCT(A)) QG3 430
RETURN QG3 440
END QG3 450