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vendor/CutTools/src/qcdloop/qllnomrat4.f
 
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      double complex function qllnomrat4(ms1,ms2,mt1,mt2)
 
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************************************************************************
 
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*     Author: R.K. Ellis                                               *
 
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*     August, 2007.                                                    *
 
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*     Lnomrat4(-s1,-s2,-t1,-t2)=                                       *
 
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*     ln(1-((ms1-i*ep)*(ms2-i*ep))/((mt1-i*ep)/(mt2-i*ep)))            *
 
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*     this function is hard-wired for sign of epsilon we must adjust   *
 
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*     sign of s1,s2,t1,t2 to get the right sign for epsilon            *
 
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************************************************************************
 
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      implicit none
 
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      include 'qlconstants.f'
 
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      double precision ms1,ms2,mt1,mt2,prod,htheta
 
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C--- define Heaviside theta function (=1 for x>0) and (0 for x < 0)
 
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      htheta(ms1)=half+half*sign(one,ms1)
 
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      prod=1d0-(ms1*ms2)/(mt1*mt2)
 
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      qllnomrat4=dcmplx(dlog(abs(prod)))
 
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     . -half*impi*dcmplx(htheta(-prod))
 
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     . *dcmplx(htheta(-ms1)+htheta(-ms2)-htheta(-mt1)-htheta(-mt2))
 
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      return
 
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      end
 
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