5,862 research outputs found
Adaptation dynamics of the quasispecies model
We study the adaptation dynamics of an initially maladapted population
evolving via the elementary processes of mutation and selection. The evolution
occurs on rugged fitness landscapes which are defined on the multi-dimensional
genotypic space and have many local peaks separated by low fitness valleys. We
mainly focus on the Eigen's model that describes the deterministic dynamics of
an infinite number of self-replicating molecules. In the stationary state, for
small mutation rates such a population forms a {\it quasispecies} which
consists of the fittest genotype and its closely related mutants. The
quasispecies dynamics on rugged fitness landscape follow a punctuated (or
step-like) pattern in which a population jumps from a low fitness peak to a
higher one, stays there for a considerable time before shifting the peak again
and eventually reaches the global maximum of the fitness landscape. We
calculate exactly several properties of this dynamical process within a
simplified version of the quasispecies model.Comment: Proceedings of Statphys conference at IIT Guwahati, to be published
in Praman
Exploring NK Fitness Landscapes Using Imitative Learning
The idea that a group of cooperating agents can solve problems more
efficiently than when those agents work independently is hardly controversial,
despite our obliviousness of the conditions that make cooperation a successful
problem solving strategy. Here we investigate the performance of a group of
agents in locating the global maxima of NK fitness landscapes with varying
degrees of ruggedness. Cooperation is taken into account through imitative
learning and the broadcasting of messages informing on the fitness of each
agent. We find a trade-off between the group size and the frequency of
imitation: for rugged landscapes, too much imitation or too large a group yield
a performance poorer than that of independent agents. By decreasing the
diversity of the group, imitative learning may lead to duplication of work and
hence to a decrease of its effective size. However, when the parameters are set
to optimal values the cooperative group substantially outperforms the
independent agents
Funnels in Energy Landscapes
Local minima and the saddle points separating them in the energy landscape
are known to dominate the dynamics of biopolymer folding. Here we introduce a
notion of a "folding funnel" that is concisely defined in terms of energy
minima and saddle points, while at the same time conforming to a notion of a
"folding funnel" as it is discussed in the protein folding literature.Comment: 6 pages, 3 figures, submitted to European Conference on Complex
Systems 200
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