Oracle-Augmented Prophet Inequalities
arxiv(2024)
摘要
In the classical prophet inequality settings, a gambler is given a sequence
of n random variables X_1, …, X_n, taken from known distributions,
observes their values in this (potentially adversarial) order, and select one
of them, immediately after it is being observed, so that its value is as high
as possible. The classical prophet inequality shows a strategy that
guarantees a value at least half of that an omniscience prophet that picks the
maximum, and this ratio is optimal.
Here, we generalize the prophet inequality, allowing the gambler some
additional information about the future that is otherwise privy only to the
prophet. Specifically, at any point in the process, the gambler is allowed to
query an oracle 𝒪. The oracle responds with a single bit answer:
YES if the current realization is greater than the remaining realizations, and
NO otherwise. We show that the oracle model with m oracle calls is equivalent
to the Top-1-of-(m+1) model when the objective is maximizing the
probability of selecting the maximum. This equivalence fails to hold when the
objective is maximizing the competitive ratio, but we still show that any
algorithm for the oracle model implies an equivalent competitive ratio for the
Top-1-of-(m+1) model.
We resolve the oracle model for any m, giving tight lower and upper bound
on the best possible competitive ratio compared to an almighty adversary. As a
consequence, we provide new results as well as improvements on known results
for the Top-1-of-m model.
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