subroutine contin(m,phi,dcut,tol,xn,yn)
*     *****************************************************************
*     take the existing curve as initial condition.
      integer m,j
      double precision xn(0:8192),yn(0:8192),phi(0:8192)
      double precision sxn(0:8192),syn(0:8192)
      double precision pi,p2,h,hp,sa,dcut,tol
      common/salpha/sa
      common/gridsz/h,hp
      common/valupi/pi,p2
  
      read(15,*) xn
      read(16,*) yn
      read(17,*) (phi(j),j=0,128)
      print *,'fine'

      call fd1(m,xn,sxn,h,dcut)
      call fd1(m,yn,syn,h,dcut)

      sa = 0.D0
      do 50 j=0,m-1
         sa = sa + dsqrt(sxn(j)**2 + syn(j)**2)
 50   continue
      sa = sa/dfloat(m)/p2
      print *,'sa=',sa

      call kfilter(m,dcut,phi)

 101  format(2(f12.6,2x))
      end