c init_circular.f
c ***********************************************************************
c 
      subroutine init_circular(n)
c Given out an initial configuration: flat circle (Wr=0)
c initialize x(i,j) as well as (f,v,u)

      implicit double precision(a-h,o-z)
      parameter(maxa=500,maxn=maxa*3,pi2=2.d0*3.1415926535d0)
      integer n
      common/matrix/x(maxa,3),bangle(maxa),rz(maxa)
      common/matrix2/ r(maxa,maxa)
      common/param/temp,bendc,r0,beadr,ss1,interval,dtime,gamma,
     +amass,am(maxn),coef,dtime2
      common/bf_coords/f(maxa,3),v(maxa,3),u(maxa,3)
      common/tor_param/dr,cg,phi0,dlk,phii,subseg

      angle = pi2/n
      radius=1.02*r0/2/sin(angle/2)

      x(1,1) = radius
      x(1,2) = 0.d0
      x(1,3) = 0.d0
      do i = 2, n
         x(i,1) = radius*cos((i-1)*angle)
         x(i,2) = radius*sin((i-1)*angle)
         x(i,3) = 0.d0
      enddo

       call update_bond(n)

c next part need to be finished when euler angle is needed
      do i = 1, n
         angle = (i-1)*phii
c set the torsional placement
         cos1 = cos(angle)
         sin1 = sin(angle)
         f(i,1) = -sin1*u(i,2)
         f(i,2) = sin1*u(i,1)
         f(i,3) = -cos1
         v(i,1) = -cos1*u(i,2)
         v(i,2) = cos1*u(i,1)
         v(i,3) = sin1
       enddo

c  the (f,v,u) systhesized by the procedure above are
c  already orthogonal
      call update_euler(n) 
      call update_rij(n)
 
      return
      end