QUANTITIES:  Numeric quantities obtainable from log files.

Several programs (eg, the xxx-plt family) deal with quantities
obtained from log files.  Each such quantity is associated with a
single character, whose meaning may be modified by a positive integer.
Such a character/modifier combination may be associated with a single
numeric value, or an array of values, as determined by the application
module.

A set of quantities is specified by a string consisting of one or more
quantity specifications of the following form:

   {letter[modifier][@[low[:[high]]]]}

I.e. each quantity specification starts with an identitying letter,
optionally followed by a non-negative integer modifier.  This may be
followed by a specification for a range of values of this type, as
indicated by the presence of an '@'.  If nothing follows the '@', the
low bound is assumed to be zero and the high bound whatever is the
maximum, or zero as well, if there is no maximum.  If the low bound
alone is specified, the high bound is assumed equal to the low bound.
If the colon is present but no high bound is given the high bound
defaults to the maximum, or to the low bound if there is no maximum.
Note that the absence of any range specification may be different from
a full range specification - the application might treat it either as
a full array or as a single-valued quantity.

The following quantity specifications are universally known (unless
redefined):

    t[n]  The index of the current iteration if no modifier is given.
          With modifier of n, equal to one plus the index minus one
          modulo n.  (Unfortunately, the usage with a modifier is
          masked by another definition for all except the 'bvg',
          'mol', and 'src' modules.)

    #[n]  An array with values equal to indexes, or equal to indexes
          modulo n if a modifier is specified.

Other quantities are as defined by the application, or by other
higher-level modules.  For documentation, see mc-quantities.doc,
net-quantities.doc, gp-quantities.doc, etc.

            Copyright (c) 1995-2007 by Radford M. Neal