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[theory-seminar] Theory lunch Thursday, w. Ramya Vinayak

Gregory Valiant gvaliant at cs.stanford.edu
Thu Aug 29 11:40:37 PDT 2019


Just a reminder about theory lunch today.  See you there!

On Mon, Aug 26, 2019 at 9:56 AM Gregory Valiant <gvaliant at cs.stanford.edu>
wrote:

> Hi Friends,
>
> Ramya will be visiting us from UW this week, and she will be giving a
> Theory lunch talk (noon, Gates 463a). Title/abstract are below.
>
> Cheers,
>
> -Greg
>
>
>
> Title:
>
> Crowd-sourced Clustering: Robust Algorithms and Query Design
>
> Abstract:
>
> We consider the problem of crowdsourced clustering – the task of
> clustering items using answers from non-expert crowd workers who can answer
> similarity-comparison queries of the type: “Are items i and j in the same
> cluster?” Since the workers on crowdsourcing platforms are not experts,
> they provide noisy answers. Further, due to budget constraints, we cannot
> make all possible comparisons between items in the dataset. Thus, it is
> important to design algorithms that can work with noise and partial data,
> and to design queries that reduce the noise in the responses.
>
> In the first part of the talk, we consider convex optimization based
> clustering algorithms which work with noisy and partially observed graphs
> and aim to recover the low-rank matrix that encodes underlying cluster
> structure. We provide explicit conditions in terms of the size and sparsity
> of clusters, and the number of observations required to guarantee
> successful recovery of the clusters. While we apply these algorithms to
> crowdsourced clustering problems, they can generally be applied to any
> partially observed graphs. In the second part, we demonstrate that random
> triangle queries (where three items are compared per query) provide less
> noisy data, as well as greater quantity of data, for a fixed query budget,
> as compared to random edge queries (where two items are compared per
> query). We extend the analysis of convex clustering algorithms to show that
> the exact recovery guarantees hold for triangle queries despite involving
> dependent edges. We complement our theoretical results with experiments on
> real datasets on Amazon Mechanical Turk.
>
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