A data structure used by tergm for tracking of limited information
about dyad edge histories.
The tergm package handles durational information attached to
network objects by way of the time and
lasttoggle network attributes. The lasttoggle data
structure is a 3-column matrix; the first two columns are tails
and heads (respectively) of dyads, and the third column is the last
time at which the dyad was toggled. The default last toggle time
is -INT_MAX/2. Last toggle times for non-edges are
periodically cleared in the C code. The time network
attribute is simply an integer, and together with the
lasttoggle data it determines the age of an extant
tie as time + 1 minus the last toggle time for that dyad.
The default value for time is 0.