function [dydt] = prob_7_5_fn(t,y)
% 
% Written by:
% -- 
% John L. Weatherwax                2006-05-29
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

% The standard oscillator problem (y''(t) = -y(t)): 
% 
dydt = [ y(2); -y(1) ];