hijing/src/gauss4.f

0001 C
0002 C
0003 C
0004 C
0005         FUNCTION GAUSS4(F,A,B,EPS)
0006         EXTERNAL F
0007         DIMENSION W(12),X(12)
0008         DATA CONST/1.0E-12/
0009         DATA W/0.1012285,.2223810,.3137067,.3623838,.0271525,
0010      &         .0622535,0.0951585,.1246290,.1495960,.1691565,
0011      &         .1826034,.1894506/
0012         DATA X/0.9602899,.7966665,.5255324,.1834346,.9894009,
0013      &         .9445750,0.8656312,.7554044,.6178762,.4580168,
0014      &         .2816036,.0950125/
0015         DELTA=CONST*ABS(A-B)
0016         GAUSS4=0.0
0017         AA=A
0018 5       Y=B-AA
0019         IF(ABS(Y).LE.DELTA) RETURN
0020 2       BB=AA+Y
0021         C1=0.5*(AA+BB)
0022         C2=C1-AA
0023         S8=0.0
0024         S16=0.0
0025         DO 1 I=1,4
0026         U=X(I)*C2
0027 1       S8=S8+W(I)*(F(C1+U)+F(C1-U))
0028         DO 3 I=5,12
0029         U=X(I)*C2
0030 3       S16=S16+W(I)*(F(C1+U)+F(C1-U))
0031         S8=S8*C2
0032         S16=S16*C2
0033         IF(ABS(S16-S8).GT.EPS*(1.+ABS(S16))) GOTO 4
0034         GAUSS4=GAUSS4+S16
0035         AA=BB
0036         GOTO 5
0037 4       Y=0.5*Y
0038         IF(ABS(Y).GT.DELTA) GOTO 2
0039         WRITE(6,7)
0040         GAUSS4=0.0
0041         RETURN
0042 7       FORMAT(1X,'GAUSS4....TOO HIGH ACURACY REQUIRED')
0043         END