  To simulate the expansion of the matter created in relativistic nuclear
collisions, codes in 3+1 dimensions are used and we are developing a new one.
To benchmark such codes, the Sod's shock tube is often used. A closely related
problem is the one-dimensional expansion of a gas into vacuum. In this paper,
we study this problem classically and relativistically with the Smoothed
Particle Method and test various techniques to improve the precision and speed
of the solution.
