      function kindex = kindx(il,jl,N,J)
%  Suppose the mesh points are ordered in each row from left to right
%  starting with the mesh points at level y=0.
%  Given a mesh point of the form (il*h,jl*h),
%  with il = N/2-J(jl+1), N/2 + J(jl+1) and 
%  jl =  0, N/2, we wish to determine the index k of that mesh point 
%  in an ordered list beginning with 1.
%  
N2 = N/2;
kk = 0;
if (jl >0)
  for l = 1:jl
    kk = kk + 2*J(l) + 1;
  end
 end
  kindex = kk + il - N2 + J(jl+1) + 1;
%           
