function [dX] = BeamDynamics( X, T )

% Ball and Beam:  Sp19 Version
% m = 1 kg
% J = 2 kg m^2

r = X(1);
q = X(2);
dr = X(3);
dq = X(4);
g = 9.8;

M = [1.4, 0; 0, 2+r*r];
B1 = r*dq*dq - g*sin(q);
B2 = T - 2*r*dr*dq - g*r*cos(q);

ddX = inv(M)*[B1; B2];
dX = [dr; dq; ddX];

end