hijing/src/gauss2.f

0001 C
0002 C
0003 C
0004         FUNCTION GAUSS2(F,A,B,EPS)
0005         EXTERNAL F
0006         DIMENSION W(12),X(12)
0007         DATA CONST/1.0E-12/
0008         DATA W/0.1012285,.2223810,.3137067,.3623838,.0271525,
0009      &         .0622535,0.0951585,.1246290,.1495960,.1691565,
0010      &         .1826034,.1894506/
0011         DATA X/0.9602899,.7966665,.5255324,.1834346,.9894009,
0012      &         .9445750,0.8656312,.7554044,.6178762,.4580168,
0013      &         .2816036,.0950125/
0014         DELTA=CONST*ABS(A-B)
0015         GAUSS2=0.0
0016         AA=A
0017 5       Y=B-AA
0018         IF(ABS(Y).LE.DELTA) RETURN
0019 2       BB=AA+Y
0020         C1=0.5*(AA+BB)
0021         C2=C1-AA
0022         S8=0.0
0023         S16=0.0
0024         DO 1 I=1,4
0025         U=X(I)*C2
0026 1       S8=S8+W(I)*(F(C1+U)+F(C1-U))
0027         DO 3 I=5,12
0028         U=X(I)*C2
0029 3       S16=S16+W(I)*(F(C1+U)+F(C1-U))
0030         S8=S8*C2
0031         S16=S16*C2
0032         IF(ABS(S16-S8).GT.EPS*(1.+ABS(S16))) GOTO 4
0033         GAUSS2=GAUSS2+S16
0034         AA=BB
0035         GOTO 5
0036 4       Y=0.5*Y
0037         IF(ABS(Y).GT.DELTA) GOTO 2
0038         WRITE(6,7)
0039         GAUSS2=0.0
0040         RETURN
0041 7       FORMAT(1X,'GAUSS2....TOO HIGH ACURACY REQUIRED')
0042         END