94,543 research outputs found
Mass distribution exponents for growing trees
We investigate the statistics of trees grown from some initial tree by
attaching links to preexisting vertices, with attachment probabilities
depending only on the valence of these vertices. We consider the asymptotic
mass distribution that measures the repartition of the mass of large trees
between their different subtrees. This distribution is shown to be a broad
distribution and we derive explicit expressions for scaling exponents that
characterize its behavior when one subtree is much smaller than the others. We
show in particular the existence of various regimes with different values of
these mass distribution exponents. Our results are corroborated by a number of
exact solutions for particular solvable cases, as well as by numerical
simulations
A functional limit theorem for the profile of -ary trees
In this paper we prove a functional limit theorem for the weighted profile of
a -ary tree. For the proof we use classical martingales connected to
branching Markov processes and a generalized version of the profile-polynomial
martingale. By embedding, choosing weights and a branch factor in a right way,
we finally rediscover the profiles of some well-known discrete time trees.Comment: Published in at http://dx.doi.org/10.1214/09-AAP640 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Growing Regression Forests by Classification: Applications to Object Pose Estimation
In this work, we propose a novel node splitting method for regression trees
and incorporate it into the regression forest framework. Unlike traditional
binary splitting, where the splitting rule is selected from a predefined set of
binary splitting rules via trial-and-error, the proposed node splitting method
first finds clusters of the training data which at least locally minimize the
empirical loss without considering the input space. Then splitting rules which
preserve the found clusters as much as possible are determined by casting the
problem into a classification problem. Consequently, our new node splitting
method enjoys more freedom in choosing the splitting rules, resulting in more
efficient tree structures. In addition to the Euclidean target space, we
present a variant which can naturally deal with a circular target space by the
proper use of circular statistics. We apply the regression forest employing our
node splitting to head pose estimation (Euclidean target space) and car
direction estimation (circular target space) and demonstrate that the proposed
method significantly outperforms state-of-the-art methods (38.5% and 22.5%
error reduction respectively).Comment: Paper accepted by ECCV 201
Martingales and Profile of Binary Search Trees
We are interested in the asymptotic analysis of the binary search tree (BST)
under the random permutation model. Via an embedding in a continuous time
model, we get new results, in particular the asymptotic behavior of the
profile
On the number of vertices of each rank in phylogenetic trees and their generalizations
We find surprisingly simple formulas for the limiting probability that the
rank of a randomly selected vertex in a randomly selected phylogenetic tree or
generalized phylogenetic tree is a given integer.Comment: 7 pages, 1 figur
Phase Transition in the Aldous-Shields Model of Growing Trees
We study analytically the late time statistics of the number of particles in
a growing tree model introduced by Aldous and Shields. In this model, a cluster
grows in continuous time on a binary Cayley tree, starting from the root, by
absorbing new particles at the empty perimeter sites at a rate proportional to
c^{-l} where c is a positive parameter and l is the distance of the perimeter
site from the root. For c=1, this model corresponds to random binary search
trees and for c=2 it corresponds to digital search trees in computer science.
By introducing a backward Fokker-Planck approach, we calculate the mean and the
variance of the number of particles at large times and show that the variance
undergoes a `phase transition' at a critical value c=sqrt{2}. While for
c>sqrt{2} the variance is proportional to the mean and the distribution is
normal, for c<sqrt{2} the variance is anomalously large and the distribution is
non-Gaussian due to the appearance of extreme fluctuations. The model is
generalized to one where growth occurs on a tree with branches and, in this
more general case, we show that the critical point occurs at c=sqrt{m}.Comment: Latex 17 pages, 6 figure
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