function U = boundary_cond(U);
% In this function, boundary conditions for the shock tube
% should be implemented
% The boundary conditions are: 
% u(0,t)=u(L,t) = 0  => rho*u = 0 at both ends
% rho should be extrapolated at both ends


%%%% Here you have to implement the boudary conditions !!!


% U(1,1)=.....
% U(end,1)=.....
% U(1,2)=.....
% U(end,2)=.....