gauss3.f

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C
C
C
        FUNCTION gauss3(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)
        gauss3=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
        gauss3=gauss3+s16
        aa=bb
        goto 5
4       y=0.5*y
        IF(abs(y).GT.delta) goto 2
        WRITE(6,7)
        gauss3=0.0
        RETURN
7       FORMAT(1x,'GAUSS3....TOO HIGH ACURACY REQUIRED')
        END