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vendor/CutTools/src/qcdloop/qlbox11.f
 
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      subroutine qlbox11(Y,musq,Ires)
 
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      implicit none
 
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C  I^{\{D=4-2 \epsilon\}}_4(0,m_3^2,\pt^2,m_4^2;s_{12},s_{23};0,0,m_3^2,m_4^2)
 
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c y11=
 
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c [                              m3sq - s12                            ]
 
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c [     0           0            ----------                0           ]
 
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c [                                  2                                 ]
 
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c [                                                                    ]
 
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c [                                                    m4sq - s23      ]
 
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c [     0           0                0                 ----------      ]
 
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c [                                                        2           ]
 
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c [                                                                    ]
 
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c [ m3sq - s12                                    - p3sq + m4sq + m3sq ]
 
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c [ ----------      0               m3sq          -------------------- ]
 
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c [     2                                                  2           ]
 
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c [                                                                    ]
 
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c [             m4sq - s23  - p3sq + m4sq + m3sq                       ]
 
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c [     0       ----------  --------------------          m4sq         ]
 
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c [                 2                2                                 ]
 
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      include 'qlconstants.f'
 
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      integer iep
 
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      logical qlzero
 
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      double precision Y(4,4),p3sq,m3sq,m4sq,musq,
 
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     . m3mu,m4mu,sibar,tabar,x43p,x43m,x43pm1,x43mm1,ieps2
 
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      double complex wlogt,wlogs,qllnrat,Ires(-2:0),Intbit,
 
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     . root,cln,ln43m,ln43p,ga43p,ga43pm1,ga43m,ga43mm1,rat2p,rat2m
 
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      m3sq=Y(3,3)
 
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      m4sq=Y(4,4)
 
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      sibar=2d0*Y(1,3)
 
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      tabar=2d0*Y(2,4)
 
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      p3sq=-(2d0*Y(3,4)-Y(3,3)-Y(4,4))
 
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      m3mu=sqrt(m3sq*musq)
 
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      m4mu=sqrt(m4sq*musq)
 
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      wlogt=qllnrat(tabar,m4mu)
 
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      wlogs=qllnrat(sibar,m3mu)
 
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C----evaluate gamma's for the case p3sq=0
 
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      if (qlzero(p3sq)) then
 
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      root=cone
 
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      x43p=-one
 
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      x43pm1=-one
 
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      x43m=m3sq
 
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      x43mm1=m4sq
 
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      else
 
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      root=dcmplx((p3sq+m3sq-m4sq)**2-4d0*m3sq*p3sq)
 
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      root=sqrt(root)
 
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      ga43p=  dcmplx(+p3sq+m3sq-m4sq)+root
 
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      ga43pm1=dcmplx(-p3sq+m3sq-m4sq)+root
 
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      ga43m=  dcmplx(+p3sq+m3sq-m4sq)-root
 
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      ga43mm1=dcmplx(-p3sq+m3sq-m4sq)-root
 
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      x43p=  -dreal(ga43p)
 
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      x43pm1=-dreal(ga43pm1)
 
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      x43m=   dreal(ga43m)
 
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      x43mm1= dreal(ga43mm1)
 
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      endif
 
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C----deal with real roots
 
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      if (qlzero(dimag(root))) then
 
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      ln43p=qllnrat(x43p,x43pm1)
 
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      ln43m=qllnrat(x43m,x43mm1)
 
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      else
 
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      call qlratgam(rat2p,rat2m,ieps2,p3sq,m4sq,m3sq)      
 
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      ln43p=cln(rat2p,ieps2)
 
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      ln43m=cln(rat2m,ieps2)
 
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      endif
 
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      if (qlzero(p3sq)) then
 
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      Intbit=-chalf*log(m3sq/m4sq)**2
 
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      else
 
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      Intbit=-chalf*(ln43p**2+ln43m**2)
 
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      endif
 
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      Ires(-2)=cone
 
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      Ires(-1)=-wlogt-wlogs
 
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      Ires( 0)=Intbit
 
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     . +ctwo*wlogt*wlogs-dcmplx(0.5d0*pisq)
 
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     . +dcmplx(0.25d0*log(m3sq/m4sq)**2)
 
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      do iep=-2,0
 
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      Ires(iep)=Ires(iep)/dcmplx(sibar*tabar)
 
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      enddo
 
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      return
 
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      end
 
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