gauss4.f

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C
C
C
C
  FUNCTION gauss4(F,A,B,EPS)
  EXTERNAL f
  dimension w(12),x(12)
  DATA const/1.0e-12/
  DATA w/0.1012285,.2223810,.3137067,.3623838,.0271525,
     &         .0622535,0.0951585,.1246290,.1495960,.1691565,
     &         .1826034,.1894506/
  DATA x/0.9602899,.7966665,.5255324,.1834346,.9894009,
     &         .9445750,0.8656312,.7554044,.6178762,.4580168,
     &         .2816036,.0950125/
  delta=const*abs(a-b)
  gauss4=0.0
  aa=a
5 y=b-aa
  IF(abs(y).LE.delta) RETURN
2 bb=aa+y
  c1=0.5*(aa+bb)
  c2=c1-aa
  s8=0.0
  s16=0.0
  DO 1 i=1,4
  u=x(i)*c2
1 s8=s8+w(i)*(f(c1+u)+f(c1-u))
  DO 3 i=5,12
  u=x(i)*c2
3 s16=s16+w(i)*(f(c1+u)+f(c1-u))
  s8=s8*c2
  s16=s16*c2
  IF(abs(s16-s8).GT.eps*(1.+abs(s16))) goto 4
  gauss4=gauss4+s16
  aa=bb
  goto 5
4 y=0.5*y
  IF(abs(y).GT.delta) goto 2
  WRITE(6,7)
  gauss4=0.0
  RETURN
7 FORMAT(1x,'GAUSS4....TOO HIGH ACURACY REQUIRED')
  END