anchor.diff:         double precision aux(1-mbc:maxmx+mbc, 1-mbc:maxmy+mbc, maux)
   
          integer i, j,mq
  -       double precision xlow, ylow, s, r2, xc,yc, w
  -       xc = 0.2d0
  -       yc = 0.21d0
  +       double precision xlow, ylow, w
   
          do mq = 1,meqn
             do i = 1-mbc,mx+mbc
  
positive.code:                 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
  
negative.code:       double precision xc,yc
        double precision xs,ys, rs
  
        xs = 0.25d0
        ys = 0.25d0
  
        rs = sqrt((xc - xs)**2 + (yc - ys)**2)
        fdisc = rs - 0.2d0
        end
  