10,167 research outputs found
Principal components analysis in the space of phylogenetic trees
Phylogenetic analysis of DNA or other data commonly gives rise to a
collection or sample of inferred evolutionary trees. Principal Components
Analysis (PCA) cannot be applied directly to collections of trees since the
space of evolutionary trees on a fixed set of taxa is not a vector space. This
paper describes a novel geometrical approach to PCA in tree-space that
constructs the first principal path in an analogous way to standard linear
Euclidean PCA. Given a data set of phylogenetic trees, a geodesic principal
path is sought that maximizes the variance of the data under a form of
projection onto the path. Due to the high dimensionality of tree-space and the
nonlinear nature of this problem, the computational complexity is potentially
very high, so approximate optimization algorithms are used to search for the
optimal path. Principal paths identified in this way reveal and quantify the
main sources of variation in the original collection of trees in terms of both
topology and branch lengths. The approach is illustrated by application to
simulated sets of trees and to a set of gene trees from metazoan (animal)
species.Comment: Published in at http://dx.doi.org/10.1214/11-AOS915 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
An Efficient Hybrid Ant Colony System for the Generalized Traveling Salesman Problem
The Generalized Traveling Salesman Problem (GTSP) is an extension of the
well-known Traveling Salesman Problem (TSP), where the node set is partitioned
into clusters, and the objective is to find the shortest cycle visiting each
cluster exactly once. In this paper, we present a new hybrid Ant Colony System
(ACS) algorithm for the symmetric GTSP. The proposed algorithm is a
modification of a simple ACS for the TSP improved by an efficient GTSP-specific
local search procedure. Our extensive computational experiments show that the
use of the local search procedure dramatically improves the performance of the
ACS algorithm, making it one of the most successful GTSP metaheuristics to
date.Comment: 7 page
On green routing and scheduling problem
The vehicle routing and scheduling problem has been studied with much
interest within the last four decades. In this paper, some of the existing
literature dealing with routing and scheduling problems with environmental
issues is reviewed, and a description is provided of the problems that have
been investigated and how they are treated using combinatorial optimization
tools
Transport optimization on complex networks
We present a comparative study of the application of a recently introduced
heuristic algorithm to the optimization of transport on three major types of
complex networks. The algorithm balances network traffic iteratively by
minimizing the maximum node betweenness with as little path lengthening as
possible. We show that by using this optimal routing, a network can sustain
significantly higher traffic without jamming than in the case of shortest path
routing. A formula is proved that allows quick computation of the average
number of hops along the path and of the average travel times once the
betweennesses of the nodes are computed. Using this formula, we show that
routing optimization preserves the small-world character exhibited by networks
under shortest path routing, and that it significantly reduces the average
travel time on congested networks with only a negligible increase in the
average travel time at low loads. Finally, we study the correlation between the
weights of the links in the case of optimal routing and the betweennesses of
the nodes connected by them.Comment: 19 pages, 7 figure
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