  For field theories with a topological charge Q, it is often of interest to
measure the topological susceptibility chi_t = ( < Q^2 > - < Q >^2 ) / V. If we
manage to perform a Monte Carlo simulation where Q changes frequently, chi_t
can be evaluated directly. However, for local update algorithms and fine
lattices, the auto-correlation time with respect to Q tends to be extremely
long, which invalidates the direct approach. Nevertheless, the measurement of
chi_t is still feasible, even when the entire Markov chain is topologically
frozen. We test a method for this purpose, based on the correlation of the
topological charge density, as suggested by Aoki, Fukaya, Hashimoto and Onogi.
Our studies in non-linear sigma-models and in 2d Abelian gauge theory yield
accurate results for chi_t, which confirm that the method is applicable. We
also obtain promising results in 4d SU(2) Yang-Mills theory, which suggest the
applicability of this method in QCD.
