  The density matrix renormalization group (DMRG) algorithm was originally
designed to efficiently compute the zero temperature or ground-state properties
of one dimensional strongly correlated quantum systems. The development of the
algorithm at finite temperature has been a topic of much interest, because of
the usefulness of thermodynamics quantities in understanding the physics of
condensed matter systems, and because of the increased complexity associated
with efficiently computing temperature-dependent properties. The ancilla method
is a DMRG technique that enables the computation of these thermodynamic
quantities. In this paper, we review the ancilla method, and improve its
performance by working on reduced Hilbert spaces and using canonical
approaches. We furthermore explore its applicability beyond spins systems to
t-J and Hubbard models.
