Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Learning Product Rankings Robust to Fake Users   In many online platforms, customers' decisions are substantially influenced
by product rankings as most customers only examine a few top-ranked products.
Concurrently, such platforms also use the same data corresponding to customers'
actions to learn how these products must be ranked or ordered. These
interactions in the underlying learning process, however, may incentivize
sellers to artificially inflate their position by employing fake users, as
exemplified by the emergence of click farms. Motivated by such fraudulent
behavior, we study the ranking problem of a platform that faces a mixture of
real and fake users who are indistinguishable from one another. We first show
that existing learning algorithms---that are optimal in the absence of fake
users---may converge to highly sub-optimal rankings under manipulation by fake
users. To overcome this deficiency, we develop efficient learning algorithms
under two informational environments: in the first setting, the platform is
aware of the number of fake users, and in the second setting, it is agnostic to
the number of fake users. For both these environments, we prove that our
algorithms converge to the optimal ranking, while being robust to the
aforementioned fraudulent behavior; we also present worst-case performance
guarantees for our methods, and show that they significantly outperform
existing algorithms. At a high level, our work employs several novel approaches
to guarantee robustness such as: (i) constructing product-ordering graphs that
encode the pairwise relationships between products inferred from the customers'
actions; and (ii) implementing multiple levels of learning with a judicious
amount of bi-directional cross-learning between levels.

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The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
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The categories of this paper are: eess
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The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
14
The categories of this paper are: math-ph
6
The categories of this paper are: astro-ph
4
The categories of this paper are: cond-mat
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The categories of this paper are: nlin
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The categories of this paper are: bayes-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc