38 lines
1.1 KiB
Fortran
38 lines
1.1 KiB
Fortran
FUNCTION rd(x,y,z)
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REAL rd,x,y,z,ERRTOL,TINY,BIG,C1,C2,C3,C4,C5,C6
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PARAMETER (ERRTOL=.05,TINY=1.e-25,BIG=4.5E21,C1=3./14.,C2=1./6.,
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*C3=9./22.,C4=3./26.,C5=.25*C3,C6=1.5*C4)
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REAL alamb,ave,delx,dely,delz,ea,eb,ec,ed,ee,fac,sqrtx,sqrty,
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*sqrtz,sum,xt,yt,zt
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if(min(x,y).lt.0..or.min(x+y,z).lt.TINY.or.max(x,y,
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*z).gt.BIG)pause 'invalid arguments in rd'
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xt=x
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yt=y
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zt=z
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sum=0.
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fac=1.
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1 continue
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sqrtx=sqrt(xt)
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sqrty=sqrt(yt)
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sqrtz=sqrt(zt)
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alamb=sqrtx*(sqrty+sqrtz)+sqrty*sqrtz
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sum=sum+fac/(sqrtz*(zt+alamb))
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fac=.25*fac
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xt=.25*(xt+alamb)
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yt=.25*(yt+alamb)
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zt=.25*(zt+alamb)
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ave=.2*(xt+yt+3.*zt)
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delx=(ave-xt)/ave
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dely=(ave-yt)/ave
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delz=(ave-zt)/ave
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if(max(abs(delx),abs(dely),abs(delz)).gt.ERRTOL)goto 1
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ea=delx*dely
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eb=delz*delz
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ec=ea-eb
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ed=ea-6.*eb
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ee=ed+ec+ec
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rd=3.*sum+fac*(1.+ed*(-C1+C5*ed-C6*delz*ee)+delz*(C2*ee+delz*(-C3*
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*ec+delz*C4*ea)))/(ave*sqrt(ave))
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return
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END
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