869 research outputs found
Incremental Clustering: The Case for Extra Clusters
The explosion in the amount of data available for analysis often necessitates
a transition from batch to incremental clustering methods, which process one
element at a time and typically store only a small subset of the data. In this
paper, we initiate the formal analysis of incremental clustering methods
focusing on the types of cluster structure that they are able to detect. We
find that the incremental setting is strictly weaker than the batch model,
proving that a fundamental class of cluster structures that can readily be
detected in the batch setting is impossible to identify using any incremental
method. Furthermore, we show how the limitations of incremental clustering can
be overcome by allowing additional clusters
Formal study of plane Delaunay triangulation
This article presents the formal proof of correctness for a plane Delaunay
triangulation algorithm. It consists in repeating a sequence of edge flippings
from an initial triangulation until the Delaunay property is achieved. To
describe triangulations, we rely on a combinatorial hypermap specification
framework we have been developing for years. We embed hypermaps in the plane by
attaching coordinates to elements in a consistent way. We then describe what
are legal and illegal Delaunay edges and a flipping operation which we show
preserves hypermap, triangulation, and embedding invariants. To prove the
termination of the algorithm, we use a generic approach expressing that any
non-cyclic relation is well-founded when working on a finite set
High posterior density ellipsoids of quantum states
Regions of quantum states generalize the classical notion of error bars. High
posterior density (HPD) credible regions are the most powerful of region
estimators. However, they are intractably hard to construct in general. This
paper reports on a numerical approximation to HPD regions for the purpose of
testing a much more computationally and conceptually convenient class of
regions: posterior covariance ellipsoids (PCEs). The PCEs are defined via the
covariance matrix of the posterior probability distribution of states. Here it
is shown that PCEs are near optimal for the example of Pauli measurements on
multiple qubits. Moreover, the algorithm is capable of producing accurate PCE
regions even when there is uncertainty in the model.Comment: TL;DR version: computationally feasible region estimator
Formal Verification of a Geometry Algorithm: A Quest for Abstract Views and Symmetry in Coq Proofs
This extended abstract is about an effort to build a formal description of a
triangulation algorithm starting with a naive description of the algorithm
where triangles, edges, and triangulations are simply given as sets and the
most complex notions are those of boundary and separating edges. When
performing proofs about this algorithm, questions of symmetry appear and this
exposition attempts to give an account of how these symmetries can be handled.
All this work relies on formal developments made with Coq and the mathematical
components library
Push sum with transmission failures
The push-sum algorithm allows distributed computing of the average on a
directed graph, and is particularly relevant when one is restricted to one-way
and/or asynchronous communications. We investigate its behavior in the presence
of unreliable communication channels where messages can be lost. We show that
exponential convergence still holds and deduce fundamental properties that
implicitly describe the distribution of the final value obtained. We analyze
the error of the final common value we get for the essential case of two nodes,
both theoretically and numerically. We provide performance comparison with a
standard consensus algorithm
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