30,327 research outputs found
From m-clusters to m-noncrossing partitions via exceptional sequences
Let W be a finite crystallographic reflection group. The generalized Catalan
number of W coincides both with the number of clusters in the cluster algebra
associated to W, and with the number of noncrossing partitions for W. Natural
bijections between these two sets are known. For any positive integer m, both
m-clusters and m-noncrossing partitions have been defined, and the cardinality
of both these sets is the Fuss-Catalan number. We give a natural bijection
between these two sets by first establishing a bijection between two particular
sets of exceptional sequences in the bounded derived category for any
finite-dimensional hereditary algebra.Comment: 25 pages: v2: added new section (section 8
Instance Space of the Number Partitioning Problem
Within the replica framework we study analytically the instance space of the
number partitioning problem. This classic integer programming problem consists
of partitioning a sequence of N positive real numbers \{a_1, a_2,..., a_N}
(the instance) into two sets such that the absolute value of the difference of
the sums of over the two sets is minimized. We show that there is an
upper bound to the number of perfect partitions (i.e. partitions
for which that difference is zero) and characterize the statistical properties
of the instances for which those partitions exist. In particular, in the case
that the two sets have the same cardinality (balanced partitions) we find
. Moreover, we show that the disordered model resulting from hte
instance space approach can be viewed as a model of replicators where the
random interactions are given by the Hebb rule.Comment: 7 page
Information Structures in Optimal Auctions
A seller wishes to sell an object to one of multiple bidders. The valuations of the bidders are privately known. We consider the joint design problem in which the seller can decide the accuracy by which bidders learn their valuation and to whom to sell at what price. We establish that optimal information structures in an optimal auction exhibit a number of properties: (i) information structures can be represented by monotone partitions, (ii) the cardinality of each partition is finite, (iii) the partitions are asymmetric across agents. These properties imply that the optimal selling strategy of a seller can be implemented by a sequence of exclusive take-it or leave-it offers.Optimal Auction, Private Values, Information Structures, Partitions
The Equity Premium Consensus Forecast Revisited
A seller wishes to sell an object to one of multiple bidders. The valuations of the bidders are privately known. We consider the joint design problem in which the seller can decide the accuracy by which bidders learn their valuation and to whom to sell at what price. We establish that optimal information structures in an optimal auction exhibit a number of properties: (i) information structures can be represented by monotone partitions, (ii) the cardinality of each partition is finite, (iii) the partitions are asymmetric across agents. These properties imply that the optimal selling strategy of a seller can be implemented by a sequence of exclusive take-it or leave-it offers.Equity premium
Sampling Scenario Set Partition Dual Bounds for Multistage Stochastic Programs
We consider multistage stochastic programming problems in which the random parameters have finite support, leading to optimization over a finite scenario set. There has been recent interest in dual bounds for such problems, of two types. One, known as expected group subproblem objective (EGSO) bounds, require solution of a group subproblem, which optimizes over a subset of the scenarios, for all subsets of the scenario set that have a given cardinality. Increasing the subset cardinality in the group subproblem improves bound quality, (EGSO bounds form a hierarchy), but the number of group subproblems required to compute the bound increases very rapidly. Another is based on partitions of the scenario set into subsets. Combining the values of the group subproblems for all subsets in a partition yields a partition bound. In this paper, we consider partitions into subsets of (nearly) equal cardinality. We show that the expected value of the partition bound over all such partitions also forms a hierarchy. To make use of these bounds in practice, we propose random sampling of partitions and suggest two enhancements to the approach: Sampling partitions that align with the multistage scenario tree structure and use of an auxiliary optimization problem to discover new best bounds based on the values of group subproblems already computed. We establish the effectiveness of these ideas with computational experiments on benchmark problems. Finally, we give a heuristic to save computational effort by ceasing computation of a partition partway through if it appears unpromising.
Entropy-based analysis of the number partitioning problem
In this paper we apply the multicanonical method of statistical physics on
the number-partitioning problem (NPP). This problem is a basic NP-hard problem
from computer science, and can be formulated as a spin-glass problem. We
compute the spectral degeneracy, which gives us information about the number of
solutions for a given cost and cardinality . We also study an extension
of this problem for partitions. We show that a fundamental difference on
the spectral degeneracy of the generalized () NPP exists, which could
explain why it is so difficult to find good solutions for this case. The
information obtained with the multicanonical method can be very useful on the
construction of new algorithms.Comment: 6 pages, 4 figure
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