+An MTPTracker is a wrapper around an MTPGraph. From the defined
+spatial topology and number of time steps, it builds a graph with one
+source, one sink, and two nodes per location and time. The edges from
+the source or to the sink, or between these pairs of nodes, are of
+length zero, and the edges between the two nodes of such a pair have
+negative lengths, equal to the opposite of the corresponding detection
+scores. This structure ensures that the trajectories computed by the
+MTPTracker will be node-disjoint, since the trajectories computed by
+the MTPGraph are edge-disjoint.