Alpern, Steve (2011) Find-and-fetch search on a tree. Operations Research, Vol.59 (No.5). pp. 1258-1268. doi:10.1287/opre.1110.0966 ISSN 0030-364X.

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Abstract

We introduce a new type of search game called the “find-and-fetch” game F(Q, O). The Hider simply picks any point H in the network Q. The Searcher starts at time zero at a given point O of Q, moving at unit speed until he reaches H (finds the Hider). Then he returns at a given speed ρ along the shortest path back to O, arriving at time R, the payoff.

This models the problem faced in many types of search, including search-and-rescue problems and foraging problems of animals (where food must be found and returned to the lair). When Q is a binary tree, we derive optimal probabilities for the Searcher to branch at the nodes. These probabilities give a positive bias towards searching longer branches first. We show that the minimax value of the return time R (the game value of F(Q, O)) is μ + D/ρ, where μ is the total length of Q and D is the mean distance from the root O to the leaves (terminal nodes) of Q, where the mean is taken with respect to what is known as the equal branch density distribution. As ρ goes to infinity, our problem reduces to the search game model where the payoff is simply the time to reach the Hider, and our results tend to those obtained by Gal [Gal, S. 1979. Search games with mobile and immobile hider. SIAM J. Control Optim. 17(1) 99–122] and Anderson and Gal [Anderson, E. J., S. Gal. 1990. Search in a maze. Probab. Engrg. Inform. Sci. 4(3) 311–318] for that model. We also apply our return time formula μ + D/ρ to determine the ideal location for the root (lair or rescue center) O, assuming it can be moved. In the traditional “find only” model, the location of O does not matter.

Item Type:	Journal Article
Divisions:	Faculty of Social Sciences > Warwick Business School > Operational Research & Management Sciences Faculty of Social Sciences > Warwick Business School
Journal or Publication Title:	Operations Research
Publisher:	Institute for Operations Research and the Management Sciences (I N F O R M S)
ISSN:	0030-364X
Official Date:	2011
Dates:	Date Event 2011 Published
Volume:	Vol.59
Number:	No.5
Page Range:	pp. 1258-1268
DOI:	10.1287/opre.1110.0966
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access

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