9,408 research outputs found
Fast Algorithms for Online Stochastic Convex Programming
We introduce the online stochastic Convex Programming (CP) problem, a very
general version of stochastic online problems which allows arbitrary concave
objectives and convex feasibility constraints. Many well-studied problems like
online stochastic packing and covering, online stochastic matching with concave
returns, etc. form a special case of online stochastic CP. We present fast
algorithms for these problems, which achieve near-optimal regret guarantees for
both the i.i.d. and the random permutation models of stochastic inputs. When
applied to the special case online packing, our ideas yield a simpler and
faster primal-dual algorithm for this well studied problem, which achieves the
optimal competitive ratio. Our techniques make explicit the connection of
primal-dual paradigm and online learning to online stochastic CP.Comment: To appear in SODA 201
First-Come-First-Served for Online Slot Allocation and Huffman Coding
Can one choose a good Huffman code on the fly, without knowing the underlying
distribution? Online Slot Allocation (OSA) models this and similar problems:
There are n slots, each with a known cost. There are n items. Requests for
items are drawn i.i.d. from a fixed but hidden probability distribution p.
After each request, if the item, i, was not previously requested, then the
algorithm (knowing the slot costs and the requests so far, but not p) must
place the item in some vacant slot j(i). The goal is to minimize the sum, over
the items, of the probability of the item times the cost of its assigned slot.
The optimal offline algorithm is trivial: put the most probable item in the
cheapest slot, the second most probable item in the second cheapest slot, etc.
The optimal online algorithm is First Come First Served (FCFS): put the first
requested item in the cheapest slot, the second (distinct) requested item in
the second cheapest slot, etc. The optimal competitive ratios for any online
algorithm are 1+H(n-1) ~ ln n for general costs and 2 for concave costs. For
logarithmic costs, the ratio is, asymptotically, 1: FCFS gives cost opt + O(log
opt).
For Huffman coding, FCFS yields an online algorithm (one that allocates
codewords on demand, without knowing the underlying probability distribution)
that guarantees asymptotically optimal cost: at most opt + 2 log(1+opt) + 2.Comment: ACM-SIAM Symposium on Discrete Algorithms (SODA) 201
Social welfare and profit maximization from revealed preferences
Consider the seller's problem of finding optimal prices for her
(divisible) goods when faced with a set of consumers, given that she can
only observe their purchased bundles at posted prices, i.e., revealed
preferences. We study both social welfare and profit maximization with revealed
preferences. Although social welfare maximization is a seemingly non-convex
optimization problem in prices, we show that (i) it can be reduced to a dual
convex optimization problem in prices, and (ii) the revealed preferences can be
interpreted as supergradients of the concave conjugate of valuation, with which
subgradients of the dual function can be computed. We thereby obtain a simple
subgradient-based algorithm for strongly concave valuations and convex cost,
with query complexity , where is the additive
difference between the social welfare induced by our algorithm and the optimum
social welfare. We also study social welfare maximization under the online
setting, specifically the random permutation model, where consumers arrive
one-by-one in a random order. For the case where consumer valuations can be
arbitrary continuous functions, we propose a price posting mechanism that
achieves an expected social welfare up to an additive factor of
from the maximum social welfare. Finally, for profit maximization (which may be
non-convex in simple cases), we give nearly matching upper and lower bounds on
the query complexity for separable valuations and cost (i.e., each good can be
treated independently)
Individual vs. Collective Bargaining in the Large Firm Search Model
We analyze the welfare and employment effects of different wage bargaining regimes. Within the large firm search model, we show that collective bargaining affects employment
via two channels. Collective bargaining exerts opposing effects on job creation and wage setting. Firms have a stronger incentive for strategic employment, while
workers benefit from the threat of a strike. We find that the employment increase due to the strategic motive is dominated by the employment decrease due to the increase in
workers' threat point. In aggregate equilibrium, employment is ineciently low under collective bargaining. But it is not always true that equilibrium wages exceed those
under individual bargaining. If unemployment benefits are sufficiently low, collectively bargained wages are smaller. The theory sheds new light on policies concerned with
strategic employment and the relation between replacement rates and the extent of collective wage bargaining
Individual vs. Collective Bargaining in the Large Firm Search Model
We analyze the welfare and employment effects of different wage bargaining regimes. Within the large firm search model, we show that collective bargaining affects employment via two channels. Collective bargaining exerts opposing effects on job creation and wage setting. Firms have a stronger incentive for strategic employment, while workers benefit from the threat of a strike. We find that the employment increase due to the strategic motive is dominated by the employment decrease due to the increase in workers' threat point. In aggregate equilibrium, employment is ineciently low under collective bargaining. But it is not always true that equilibrium wages exceed those under individual bargaining. If unemployment benefits are sufficiently low, collectively bargained wages are smaller. The theory sheds new light on policies concerned with strategic employment and the relation between replacement rates and the extent of collective wage bargaining.search; overemployment; collective wage bargaining; wage determination
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