anchor.diff:    160          continue
   c
   c     # split the right-going flux difference into down-going and up-going:
  -      call rpt2(ixy,maxm,meqn,mwaves,mbc,mx,
  +      call rpt2(ixy,2,maxm,meqn,mwaves,maux,mbc,mx,
        &          q1d,q1d,aux1,aux2,aux3,
  -     &          2,apdq,bmasdq,bpasdq)
  +     &          apdq,bmasdq,bpasdq)
   c
   c     # modify flux below and above by B^- A^+ Delta q and  B^+ A^+ Delta q:
         do 180 m=1,meqn
  
positive.code: c
  c
  c     # split the left-going flux difference into down-going and up-going:
        call rpt2(ixy,maxm,meqn,mwaves,mbc,mx,
       &          q1d,q1d,aux1,aux2,aux3,
       &          1,amdq,bmasdq,bpasdq)
  c
  c     # modify flux below and above by B^- A^- Delta q and  B^+ A^- Delta q:
        do 160 m=1,meqn
  
negative.code: c
         if (method(3).eq.0) go to 999   !# no transverse propagation
  c
         if (method(2).gt.1 .and. method(3).eq.2) then
  c         # incorporate cqxx into amdq and apdq so that it is split also.
            do 150 i = 1, mx+1
               do 150 m=1,meqn
  