    XXX-GENP:  Generate random momentum variables.

    There is a version of this program for each 'mc' application (eg,
    net-genp).  It is not usually necessary to run this program, since
    xxx-mc generates momentum variables automatically if they don't
    already exist but are needed for the current Markov chain operations.
    However, xxx-genp is needed to implement xxx-circ, since the automatic
    generation disturbs random number synchronization.

    Usage:

        xxx-genp log-file

    Here, 'xxx' is a prefix identifying the particular incarnaton of this
    program (eg, 'dist' or 'net').

    If the last mc-spec command (see mc-spec.doc) uses operations that
    require momentum variables, this program generates random values for
    the momenta, and appends these values to the log file, with index the
    same as the index of the last record currently in the log file.

    If no mc-spec command has been done, or the last such command involved
    only operations that don't require momentum, the xxx-genp command
    silently does nothing.  This is the behaviour needed to implement
    xxx-circ (see xxx-circ.doc).

                Copyright (c) 1995-2003 by Radford M. Neal