%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%    Solve the equations for the Swinging Spring
%    in the case of resonance
%
%    This file is for the rate of change (roc) function
%    for the pendulum in 3 dimensions.
%
%    Calculate the rate of change of xvector, where
%         xvector = (x,xdot,y,ydot,z,zdot).
% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function xdot=roc3d(t,x)
global m 
global g 
global k 
global l 
global l_0 
global epsilon 
global epssq 
global omega_Z 
global omega_R
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
r=sqrt(x(1)^2+x(3)^2+x(5)^2);
fac=omega_Z^2*(r-l_0)/r;
xdot(1) = x(2);
xdot(2) = - fac*x(1);
xdot(3) = x(4);
xdot(4) = - fac*x(3);
xdot(5) = x(6);
xdot(6) = - fac*x(5) - g;
end