anchor.diff:  
         do mq = 1,meqn
            do j = 1,my
  -c           # Left edge - "this" grid is right grid; 
  -c           # "neighbor" grid is left grid.          
  -            deltam = fmneighbor0(j,mq)  + efneighbor0(j,mq,1)
  -
  -c           # Right edge                         
  +            deltam = fmneighbor0(j,mq) + efneighbor0(j,mq,1)
               deltap = fpneighbor1(j,mq) - efneighbor1(j,mq,1)
   
  -            qneighbor_dummy(0,j,mq) = -deltam
  +            qneighbor_dummy(0,j,mq)    = -deltam
               qneighbor_dummy(mx+1,j,mq) = -deltap
            enddo
   
  
positive.code:         idir = 0
           do k = 0,1
              do m = 1,maux
                 auxvec(m) = aux(1-k,j,m)
              enddo
              do m = 1,meqn
                 qvec(m) = q(1-k,j,m)
  
negative.code:          idir = 1
           do k = 0,1
              do m = 1,maux
                 auxvec(m) = aux(i,1,m)
              enddo
              do m = 1,meqn
                 qvec(m) = q(i,1-k,m)
  