Memory Lower Bounds for Randomized Collaborative Search and Applications to Biology

TL;DR

This paper investigates the minimum memory requirements for probabilistic agents in collaborative search tasks, establishing fundamental lower bounds that connect memory size with search efficiency, with implications for understanding biological systems.

Contribution

It provides the first non-trivial lower bounds on memory size needed for probabilistic searchers to achieve specific performance levels.

Findings

Lower bounds on memory size are established for efficient search.

Achieving near-optimal search time requires at least logarithmic memory in the number of agents.

Results connect computational memory limits with biological collective behavior.

Abstract

Initial knowledge regarding group size can be crucial for collective performance. We study this relation in the context of the {\em Ants Nearby Treasure Search (ANTS)} problem \cite{FKLS}, which models natural cooperative foraging behavior such as that performed by ants around their nest. In this problem, $k$ (probabilistic) agents, initially placed at some central location, collectively search for a treasure on the two-dimensional grid. The treasure is placed at a target location by an adversary and the goal is to find it as fast as possible as a function of both $k$ and $D$, where $D$ is the (unknown) distance between the central location and the target. It is easy to see that $T=\Omega(D+D^2/k)$ time units are necessary for finding the treasure. Recently, it has been established that $O(T)$ time is sufficient if the agents know their total number $k$ (or a constant approximation of it), and enough memory bits are available at their disposal \cite{FKLS}. In this paper, we establish lower bounds on the agent memory size required for achieving certain running time performances. To the best our knowledge, these bounds are the first non-trivial lower bounds for the memory size of probabilistic searchers. For example, for every given positive constant $\epsilon$, terminating the search by time $O(\log^{1-\epsilon} k \cdot T)$ requires agents to use $\Omega(\log\log k)$ memory bits. Such distributed computing bounds may provide a novel, strong tool for the investigation of complex biological systems.