XXX-WRAP:  Create a wrapped-around chain from an existing simulation run.

There is a version of this program for each 'mc' application (eg,
net-wrap).  Each version uses circular coupling to create a
wrapped-around chain, given the log file for a standard simulation
run.  If this succeeds, the iterations in the resulting log file will
all be usable, without the need to discard a burn-in period.  

Usage:

    xxx-wrap old-log-file new-log-file [ start-index ]

The old-log-file should contain iterations of a Markov chain that was
simulated using module <xxx> (eg, dist, net, gp, mix).  This
simulation will be used in creating a wrapped-around chain stored in
new-log-file (whose previous contents, if any, will be overwritten).

The wrapped-around chain is created by first copying the last
iteration in old-log-file to new-log-file, storing it at index
start-index (which defaults to 1).  This is used as the start state in
a re-running of the simulation, using the random number state and
Markov chain operations stored at start-index in old-log-file.  If no
Markov chain operations are stored at start-index, those stored at
index 0 will be used, but any stored between index 0 and start-index
will be ignored.

The simulation is rerun using the xxx-mc program, with the -c option
being used to couple with old-log-file.  This simulation will
terminate early if the next state generated is the same as the
corresponding state in old-log-file, with the remaining iterations
being simply copied from old-log-file.  If such coalescence to the
same state as before occurs, the xxx-wrap program terminates
successfully (with exit code 0), and a message giving the number of
iterations needed to produce coalescence is displayed on standard
error.  If coalescence does not occur, a message to this effect is
displayed on standard error, and the xxx-wrap program terminates with
exit code 1 (indicating failure).

            Copyright (c) 2000 by Radford M. Neal