  Quantum Monte Carlo methods are powerful techniques for studying strongly
interacting Fermi systems. However, implementing these methods on computers
with finite-precision arithmetic requires careful attention to numerical
stability. In the auxiliary-field Monte Carlo (AFMC) method, low-temperature or
large-model-space calculations require numerically stabilized matrix
multiplication. When adapting methods used in the grand-canonical ensemble to
the canonical ensemble of fixed particle number, the numerical stabilization
increases the number of required floating-point operations for computing
observables by a factor of the size of the single-particle model space, and
thus can greatly limit the systems that can be studied. We describe an improved
method for stabilizing canonical-ensemble calculations in AFMC that exhibits
better scaling, and present numerical tests that demonstrate the accuracy and
improved performance of the method.
