NUMERICAL-ANALYSIS OF MOMENTS EXPANSIONS

We present numerical results for the estimate of the ground state ener gy for two quantum many-body systems using the connected moments expan sion (CMX) and a newly developed alternate moments expansion (AMX). Co mparisons are made with an equivalent Lanczos scheme which yields a va riational upper bound for the ground state energy. For each system, th e utility of both expansions is evaluated as they pertain to relevant regions of parameter space. A brief description of the (numerical) nat ure of the singularities which may arise in the series expansions is a lso given.