anchor.diff:                  ylow = ylower + (j-1)*dy
                   call cellave2(xlow,ylow,dx,dy,w)
                   q(i,j,mq) = w
  -
  -
  -c                s = 0.5d0
  -c                if (xi .lt. s) then
  -c                   q(i,j,mq) = 0.d0
  -c                else
  -c                   q(i,j,mq) = 1.d0
  -c                endif
   
                enddo
             enddo
  
positive.code:       double precision xc,yc
        double precision xs,ys, rs
  
        xs = 0.5d0
        ys = 0.5d0
  
        rs = sqrt((xc - xs)**2 + (yc - ys)**2)
  
  
        fdisc = rs - 0.25d0
        end
  
negative.code:        double precision aux(1-mbc:maxmx+mbc, 1-mbc:maxmy+mbc, maux)
  
         integer i, j,mq
         double precision xlow, ylow, w
  
         do mq = 1,meqn
            do i = 1-mbc,mx+mbc
  