function zdot = systems_rhs( t, z )   
% systems_rhs evaluates the right hand side of the ODE that is being
% solved.   

% ODE23 calls this function many times when finding its numerical
% solution to the ODEs.

global C1 C2   % this matches the global command in the script file.

% The next two lines define the system of equations to be solved.
% They would be three lines for a third order system, etc.

zdot(1) = C1 *( ( z(2) ) ) ;
zdot(2) = C2 * ( - sin(z(1)) -.1*z(1) + 10* sin(t)  )  ; 

end    % optional end statement