function yprime = chemical_ode ( x, y )
%
%  function yprime = chemical_ode ( x, y )
%
%  computes the derivative for the chemical ODE:
%
%    Y'' = lambda * E^Y
%
lambda = - 1.0;
temp = lambda * exp ( y(1) );
yprime = [ y(2); 
           temp ];

