function zdot = myrhs(t,z,p)
%Calculates zdot from z and p and EOM
%Inputs: 
%   t       time
%   z       state
%   p       parameters struct
%Outpus:
%   zdot    rate of change of state at time t

%unpack z
x = z(1); y = z(2); xdot = z(3); ydot = z(4); 

%unpack parameters
g = p.g; m = p.m;

%myrhs
xddot = 0;
yddot = -g; 

%pack up zdot
zdot = [xdot;ydot;xddot;yddot];
end