The Broad Histogram Method (BHM) allows one to determine the energy
degeneracy g(E), i.e. the energy spectrum of a given system, from the knowledge
of the microcanonical averages and of two macroscopic
quantities Nup and Ndn defined within the method. The fundamental BHM equation
relating g(E) to the quoted averages is exact and completely general for any
conceivable system. Thus, the only possible source of numerical inaccuracies
resides on the measurement of the averages themselves. In this text, we
introduce a Monte Carlo recipe to measure microcanonical averages. In order to
test its performance, we applied it to the Ising ferromagnet on a 32x32 square
lattice. The exact values of g(E) are known up to this lattice size, thus it is
a good standard to compare our numerical results with. Measuring the deviations
relative to the exactly known values, we verified a decay proportional to
1/sqrt(counts), by increasing the counter (counts) of averaged samples over at
least 6 decades. That is why we believe this microcanonical simulator presents
no bias besides the normal statistical fluctuations. For counts~10**10, we
measured relative deviations near 10**(-5) for both g(E) and the specific heat
peak, obtained through BHM relation.Comment: 9 pages, plain tex, 3 PS figure
