An edgelist matrix. Each row is assumed to be of the form (from_node_id to_node_id time_stamp). For a directed network ,from_node_id is the id of the source node and to_node_id is the id of the destination node. For an undirected network, the order is ignored and from_node_id and to_node_id are the ids of two ends. time_stamp is the arrival time of the edge. from_node_id and to_node_id are assumed to be integers that are at least \(0\). The whole ids need not to be contiguous.
To register a new node \(i\) at time \(t\) without any edge, add a row with format (i -1 t). This works for both undirected and directed networks.
time_stamp can be either numeric or string. The value of a time-stamp can be arbitrary, but we assume that a smaller time_stamp (regarded so by the sort function in R) represents an earlier arrival time. Examples of time-stamps that satisfy this assumption are the integer 0:T, the string format `yyyy-mm-dd', and the POSIX time.