A problem with Monte Carlo (MC) simulation is that the error decreases only
as , so
need to do 100 times more work to get one more significant figure accuracy.
Unfortunately, things are even worse. Error is only for **N**
* independent* measurements. But MC configurations are usually
correlated --- depends on .

Measure the * autocorrelation function*
(similar to correlation function except in computer time, not real space)
for an operator (measurement) **A**:

is the (exponential) * autocorrelation time*,
and is equivalent to
the which measures equilibration time of the Markov process.
Need to thermalize for time .

Paul Coddington, Northeast Parallel Architectures Center at Syracuse University, paulc@npac.syr.edu