subroutine inifrt(pf,rin,nx,ny)
*****************************************************
c     initialize the level set function
*****************************************************
      integer i,j,nx,ny
      double precision pf(0:nx+1,0:ny+1)
      double precision h,hinv,x,y,r,rin
      common/meshsz/h,hinv
      do 10 j=0,ny+1
         y = (dfloat(j)-0.5D0)*h
      do 10 i=0,nx+1
         x = (dfloat(i)-0.5D0)*h
         r = dsqrt( (x-0.5D0)**2 + (y-0.5D0)**2 )
         pf(i,j) = rin - r
 10   continue
         
      end