  In this paper we present two new numerical methods for studying thermodynamic
quantities of integrable models. As an example of the effectiveness of these
two approaches, results from numerical solutions of all sets of Bethe ansatz
equations, for small Heisenberg chains, and Monte Carlo simulations in
quasi-momentum space, for a relatively larger chains, are presented. Our
results agree with those obtained by thermodynamics Bethe ansatz (TBA) and
Quantum Transfer Matrix (QTM).
