🤖 AI Summary
This study addresses the prediction problem involving six or more experts, demonstrating that traditional single ranking-based adversary strategies fail to achieve global optimality. Leveraging game theory, asymptotic analysis, and combinatorial optimization, we rigorously prove under both geometric stopping and finite-horizon settings that no single ranking strategy is globally optimal for multi-expert prediction. By introducing leading-order correction terms, this work reveals intrinsic connections among optimal strategies across varying expert pool sizes and precisely characterizes the set of optimal strategies for the five-expert case. Ultimately, this research confirms the fundamental limitations of ranking-based strategies in multi-expert scenarios, providing critical theoretical foundations for designing superior prediction algorithms.
📝 Abstract
We prove that no single rank ordered adversary strategy is globally optimal for the prediction with expert advice problem with six or more experts, in both the geometric stopping and finite time horizon settings. The proof is based on establishing a leading order correction when one expert moves far ahead of the others. This allows us to connect optimal strategies between $n$ and $j<n$ experts and utilize recent results on the exact optimality set for the five expert problem.