function rhs = Fpendula(t,y)

%
%  save file as Fpendula.m
%     - right-side forcing for ode45 solver
%

rhs = zeros(size(y));

rhs(1) =  y(2);
rhs(2) = -(1.1)*y(1) + (0.1)*y(3);
rhs(3) =  y(4);
rhs(4) =  (0.1)*y(1) - (1.1)*y(3);