function vprime = harmosc(t,vin)

global c;
global m;
%global b;
global k;


x = vin(1);
y = vin(2);

% compute derivatives for predator-prey model
% from K Tung p. 166

xprime = y;
yprime = -(k/m)*x - (c/m)*y;

% map back to vector format
vprime=[xprime;yprime];

end