Nn = 100;
  Vt = (vna-vk)*[0:Nn-1]/Nn+vk;

   Wn = 1-0.5*(1.+tanh((Vt-vh)/kh));
  
   Vn = gk*(Vt-vk)./(gna*Vt.^2.*(vna-Vt));
wrange = [0 1.1 0 1.2];
