function dydx = fcn_deut(x, y)
% Function fcn_deut evaluates derivatives for toy deuteron problem.
   global x0  E;

   dydx = ones(2,1);

   dydx(1,1) = y(2);
   if x <= x0 
      dydx(2,1) = (-1 - E) * y(1);
   else
      dydx(2,1) = -E * y(1);
   end
end
