program checkv
      integer i,j,nx,ny
      parameter(nx=64,ny=64)
      double precision h,x,y,urad,r
      double precision u(nx,ny),v(nx,ny)
      h = 1.D0/64.D0    

      do 5 j=1,ny
         y = (dble(j)-0.5D0)*h-0.5D0
      do 5 i=1,nx
         x = (dble(i)-0.5D0)*h-0.5D0
         r = dsqrt(x*x + y*y)
         u(i,j) = -urad(r)*y/r
         v(i,j) =  urad(r)*x/r
 5    continue
      read(21,101) ((u(i,j),i=1,nx),j=1,ny)
      read(21,101) ((v(i,j),i=1,nx),j=1,ny)
      write(22,102) (dble(j),dsqrt(v(j,j)**2+u(j,j)**2),j=1,64)
*     *****************************************************
 101  format(e16.10)
 102  format(2(f12.8,2x))
      end


      function urad(r)
      double precision urad,r,u0,eps
      parameter (eps=5.D-2,u0=0.07*eps)
      if( r .le. eps ) then
         urad = u0/eps
      else 
         urad = u0/r
      endif
      end