C QG2 10
C ..................................................................QG2 20
C QG2 30
C SUBROUTINE QG2 QG2 40
C QG2 50
C PURPOSE QG2 60
C TO COMPUTE INTEGRAL(FCT(X), SUMMED OVER X FROM XL TO XU) QG2 70
C QG2 80
C USAGE QG2 90
C CALL QG2 (XL,XU,FCT,Y) QG2 100
C PARAMETER FCT REQUIRES AN EXTERNAL STATEMENT QG2 110
C QG2 120
C DESCRIPTION OF PARAMETERS QG2 130
C XL - THE LOWER BOUND OF THE INTERVAL. QG2 140
C XU - THE UPPER BOUND OF THE INTERVAL. QG2 150
C FCT - THE NAME OF AN EXTERNAL FUNCTION SUBPROGRAM USED. QG2 160
C Y - THE RESULTING INTEGRAL VALUE. QG2 170
C QG2 180
C REMARKS QG2 190
C NONE QG2 200
C QG2 210
C SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED QG2 220
C THE EXTERNAL FUNCTION SUBPROGRAM FCT(X) MUST BE FURNISHED QG2 230
C BY THE USER. QG2 240
C QG2 250
C METHOD QG2 260
C EVALUATION IS DONE BY MEANS OF 2-POINT GAUSS QUADRATURE QG2 270
C FORMULA, WHICH INTEGRATES POLYNOMIALS UP TO DEGREE 3 QG2 280
C EXACTLY. QG2 290
C FOR REFERENCE, SEE QG2 300
C V.I.KRYLOV, APPROXIMATE CALCULATION OF INTEGRALS, QG2 310
C MACMILLAN, NEW YORK/LONDON, 1962, PP.100-111 AND 337-338. QG2 320
C QG2 330
C ..................................................................QG2 340
C QG2 350
SUBROUTINE QG2(XL,XU,FCT,Y) QG2 360
C QG2 370
C QG2 380
A=.5*(XU+XL) QG2 390
B=XU-XL QG2 400
Y=.2886751*B QG2 410
Y=.5*B*(FCT(A+Y)+FCT(A-Y)) QG2 420
RETURN QG2 430
END QG2 440