268 research outputs found
Shortest-weight paths in random regular graphs
Consider a random regular graph with degree and of size . Assign to
each edge an i.i.d. exponential random variable with mean one. In this paper we
establish a precise asymptotic expression for the maximum number of edges on
the shortest-weight paths between a fixed vertex and all the other vertices, as
well as between any pair of vertices. Namely, for any fixed , we show
that the longest of these shortest-weight paths has about
edges where is the unique solution of the equation , for .Comment: 20 pages. arXiv admin note: text overlap with arXiv:1112.633
The diameter of weighted random graphs
In this paper we study the impact of random exponential edge weights on the
distances in a random graph and, in particular, on its diameter. Our main
result consists of a precise asymptotic expression for the maximal weight of
the shortest weight paths between all vertices (the weighted diameter) of
sparse random graphs, when the edge weights are i.i.d. exponential random
variables.Comment: Published at http://dx.doi.org/10.1214/14-AAP1034 in the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Bootstrap percolation in inhomogeneous random graphs
A bootstrap percolation process on a graph G is an "infection" process which
evolves in rounds. Initially, there is a subset of infected nodes and in each
subsequent round every uninfected node which has at least r infected neighbours
becomes infected and remains so forever. The parameter r > 1 is fixed.
We consider this process in the case where the underlying graph is an
inhomogeneous random graph whose kernel is of rank 1. Assuming that initially
every vertex is infected independently with probability p > 0, we provide a law
of large numbers for the number of vertices that will have been infected by the
end of the process.
We also focus on a special case of such random graphs which exhibit a
power-law degree distribution with exponent in (2,3). The first two authors
have shown the existence of a critical function a_c(n) such that a_c(n)=o(n)
with the following property. Let n be the number of vertices of the underlying
random graph and let a(n) be the number of the vertices that are initially
infected. Assume that a set of a(n) vertices is chosen randomly and becomes
externally infected. If a(n) << a_c(n), then the process does not evolve at
all, with high probability as n grows, whereas if a(n)>> a_c(n), then with high
probability the final set of infected vertices is linear.
Using the techniques of the previous theorem, we give the precise asymptotic
fraction of vertices which will be eventually infected when a(n) >> a_c (n) but
a(n) = o(n). Note that this corresponds to the case where p approaches 0.Comment: 42 page
Optimal Network Compression
This paper introduces a formulation of the optimal network compression
problem for financial systems. This general formulation is presented for
different levels of network compression or rerouting allowed from the initial
interbank network. We prove that this problem is, generically, NP-hard. We
focus on objective functions generated by systemic risk measures under shocks
to the financial network. We use this framework to study the (sub)optimality of
the maximally compressed network. We conclude by studying the optimal
compression problem for specific networks; this permits us to study, e.g., the
so-called robust fragility of certain network topologies more generally as well
as the potential benefits and costs of network compression. In particular,
under systematic shocks and heterogeneous financial networks the robust
fragility results of Acemoglu et al. (2015) no longer hold generally.Comment: 34 pages, 10 figure
Bootstrap percolation in power-law random graphs
A bootstrap percolation process on a graph is an "infection" process
which evolves in rounds. Initially, there is a subset of infected nodes and in
each subsequent round each uninfected node which has at least infected
neighbours becomes infected and remains so forever. The parameter is
fixed. Such processes have been used as models for the spread of ideas or
trends within a network of individuals.
We analyse bootstrap percolation process in the case where the underlying
graph is an inhomogeneous random graph, which exhibits a power-law degree
distribution, and initially there are randomly infected nodes. The main
focus of this paper is the number of vertices that will have been infected by
the end of the process. The main result of this work is that if the degree
sequence of the random graph follows a power law with exponent , where
, then a sublinear number of initially infected vertices is
enough to spread the infection over a linear fraction of the nodes of the
random graph, with high probability.
More specifically, we determine explicitly a critical function such
that with the following property. Assuming that is the number
of vertices of the underlying random graph, if , then the
process does not evolve at all, with high probability as grows, whereas if
, then there is a constant \eps>0 such that, with high
probability, the final set of infected vertices has size at least \eps n. It
turns out that when the maximum degree is , then
depends also on . But when the maximum degree is , then .Comment: 23 page
Including Physics in Deep Learning -- An example from 4D seismic pressure saturation inversion
Geoscience data often have to rely on strong priors in the face of
uncertainty. Additionally, we often try to detect or model anomalous sparse
data that can appear as an outlier in machine learning models. These are
classic examples of imbalanced learning. Approaching these problems can benefit
from including prior information from physics models or transforming data to a
beneficial domain. We show an example of including physical information in the
architecture of a neural network as prior information. We go on to present
noise injection at training time to successfully transfer the network from
synthetic data to field data.Comment: 5 pages, 5 figures, workshop, extended abstract, EAGE 2019 Workshop
Programme, European Association of Geoscientists and Engineer
Control of interbank contagion under partial information
International audienceWe consider a stylized core-periphery financial network in which links lead to the creation of projects in the outside economy but make banks prone to contagion risk. The controller seeks to maximize, under budget constraints, the value of the financial system defined as the total amount of external projects. Under partial information on interbank links, revealed in conjunction with the spread of contagion, the optimal control problem is shown to become a Markov decision problem. We find the optimal intervention policy using dynamic programming. Our numerical results show that the value of the system depends on the connectivity in a non- monotonous way: it first increases with connectivity and then decreases with connectivity. The maximum value attained depends critically on the budget of the controller and the availability of an adapted intervention strategy. Moreover, we show that for highly connected systems, it is optimal to increase the rate of intervention in the peripheral banks rather than in core banks. Keywords: Systemic risk, Optimal control, Financial networks
Duration-dependent stochastic fluid processes and solar energy revenue modeling
We endow the classical stochastic fluid process with a duration-dependent
Markovian arrival process (DMArP). We show that this provides a flexible model
for the revenue of a solar energy generator. In particular, it allows for
heavy-tailed interarrival times and for seasonality embedded into the
state-space. It generalizes the calendar-time inhomogeneous stochastic fluid
process. We provide descriptors of the first return of the revenue process. Our
main contribution is based on the uniformization approach, by which we reduce
the problem of computing the Laplace transform to the analysis of the process
on a stochastic Poissonian grid. Since our process is duration dependent, our
construction relies on translating duration form its natural grid to the
Poissonian grid. We obtain the Laplace transfrom of the project value based on
a novel concept of -bridge and provide an efficient algorithm for computing
the duration-level density of the -bridge. Other descriptors such as the
Laplace transform of the ruin process are further provided
Decentralized Prediction Markets and Sports Books
Prediction markets allow traders to bet on potential future outcomes. These
markets exist for weather, political, sports, and economic forecasting. Within
this work we consider a decentralized framework for prediction markets using
automated market makers (AMMs). Specifically, we construct a liquidity-based
AMM structure for prediction markets that, under reasonable axioms on the
underlying utility function, satisfy meaningful financial properties on the
cost of betting and the resulting pricing oracle. Importantly, we study how
liquidity can be pooled or withdrawn from the AMM and the resulting
implications to the market behavior. In considering this decentralized
framework, we additionally propose financially meaningful fees that can be
collected for trading to compensate the liquidity providers for their vital
market function
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