Searching for an agent who may or may not want to be found

There is an extensive theory regarding optimal continuous path search for a mobile or immobile ‘target’. The traditional theory assumes that the target is one of three types: (i) an object with a known distribution of paths, (ii) a mobile or immobile hider who wants to avoid or delay capture, or (iii) a rendezvouser who wants to find the searcher. This paper introduces a new type of search problem by assuming that aims of the target are not known to the searcher. The target may be either a type (iii) cooperator (with a known cooperation probability c) or a type (ii) evader. This formulation models search problems like that for a lost teenager who may be a ‘runaway’, or a lost intelligence agent who may be a defector. In any given search context, it produces a continuum of search problems Γ(c), 0 ≤ c ≤ 1, linking a zero-sum search game (with c = 0) to a rendezvous problem (with c = 1). These models thus provide a theoretical bridge between two previously distinct parts of search theory, namely search games and rendezvous search.