  Gathering is a fundamental task for multi-agent systems and the problem has
been studied under various assumptions on the sensing capabilities of mobile
agents. This paper addresses the problem for a group of agents that are
identical and indistinguishable, oblivious, and lack the capacity of direct
communication. At the beginning of unit-time intervals, the agents select
random headings in the plane and then detect the presence of other agents
behind them. Then they move forward only if no agents are detected in their
sensing "back half-plane". Two types of motion are considered: when no peers
are detected behind them, either the agents perform unit jumps forward, or they
start to move with unit speed while continuously sensing their back half-plane,
and stop whenever another agent appears there. For the first type of motion
extensive empirical evidence suggests that with high probability clustering
occurs in finite expected time to a small region with diameter of about the
size of the unit jump, while for continuous sensing and motion we can prove
gathering in finite expected time if a "blind-zone" is assumed in their sensing
half-plane. Relationships between the number of agents or the size of the
blind-zone and convergence time are empirically studied and compared to a
theoretical upper-bound dependent on these factors.
