682 research outputs found
Identification of neutral biochemical network models from time series data
<p>Abstract</p> <p>Background</p> <p>The major difficulty in modeling biological systems from multivariate time series is the identification of parameter sets that endow a model with dynamical behaviors sufficiently similar to the experimental data. Directly related to this parameter estimation issue is the task of identifying the structure and regulation of ill-characterized systems. Both tasks are simplified if the mathematical model is canonical, <it>i.e</it>., if it is constructed according to strict guidelines.</p> <p>Results</p> <p>In this report, we propose a method for the identification of admissible parameter sets of canonical S-systems from biological time series. The method is based on a Monte Carlo process that is combined with an improved version of our previous parameter optimization algorithm. The method maps the parameter space into the network space, which characterizes the connectivity among components, by creating an ensemble of decoupled S-system models that imitate the dynamical behavior of the time series with sufficient accuracy. The concept of sloppiness is revisited in the context of these S-system models with an exploration not only of different parameter sets that produce similar dynamical behaviors but also different network topologies that yield dynamical similarity.</p> <p>Conclusion</p> <p>The proposed parameter estimation methodology was applied to actual time series data from the glycolytic pathway of the bacterium <it>Lactococcus lactis </it>and led to ensembles of models with different network topologies. In parallel, the parameter optimization algorithm was applied to the same dynamical data upon imposing a pre-specified network topology derived from prior biological knowledge, and the results from both strategies were compared. The results suggest that the proposed method may serve as a powerful exploration tool for testing hypotheses and the design of new experiments.</p
EEF: Exponentially Embedded Families with Class-Specific Features for Classification
In this letter, we present a novel exponentially embedded families (EEF)
based classification method, in which the probability density function (PDF) on
raw data is estimated from the PDF on features. With the PDF construction, we
show that class-specific features can be used in the proposed classification
method, instead of a common feature subset for all classes as used in
conventional approaches. We apply the proposed EEF classifier for text
categorization as a case study and derive an optimal Bayesian classification
rule with class-specific feature selection based on the Information Gain (IG)
score. The promising performance on real-life data sets demonstrates the
effectiveness of the proposed approach and indicates its wide potential
applications.Comment: 9 pages, 3 figures, to be published in IEEE Signal Processing Letter.
IEEE Signal Processing Letter, 201
Consensus-based control for a network of diffusion PDEs with boundary local interaction
In this paper the problem of driving the state of a network of identical
agents, modeled by boundary-controlled heat equations, towards a common
steady-state profile is addressed. Decentralized consensus protocols are
proposed to address two distinct problems. The first problem is that of
steering the states of all agents towards the same constant steady-state
profile which corresponds to the spatial average of the agents initial
condition. A linear local interaction rule addressing this requirement is
given. The second problem deals with the case where the controlled boundaries
of the agents dynamics are corrupted by additive persistent disturbances. To
achieve synchronization between agents, while completely rejecting the effect
of the boundary disturbances, a nonlinear sliding-mode based consensus protocol
is proposed. Performance of the proposed local interaction rules are analyzed
by applying a Lyapunov-based approach. Simulation results are presented to
support the effectiveness of the proposed algorithms
On Learning Mixtures of Well-Separated Gaussians
We consider the problem of efficiently learning mixtures of a large number of
spherical Gaussians, when the components of the mixture are well separated. In
the most basic form of this problem, we are given samples from a uniform
mixture of standard spherical Gaussians, and the goal is to estimate the
means up to accuracy using samples.
In this work, we study the following question: what is the minimum separation
needed between the means for solving this task? The best known algorithm due to
Vempala and Wang [JCSS 2004] requires a separation of roughly
. On the other hand, Moitra and Valiant [FOCS 2010] showed
that with separation , exponentially many samples are required. We
address the significant gap between these two bounds, by showing the following
results.
1. We show that with separation , super-polynomially many
samples are required. In fact, this holds even when the means of the
Gaussians are picked at random in dimensions.
2. We show that with separation ,
samples suffice. Note that the bound on the separation is independent of
. This result is based on a new and efficient "accuracy boosting"
algorithm that takes as input coarse estimates of the true means and in time
outputs estimates of the means up to arbitrary accuracy
assuming the separation between the means is (independently of ).
We also present a computationally efficient algorithm in dimensions
with only separation. These results together essentially
characterize the optimal order of separation between components that is needed
to learn a mixture of spherical Gaussians with polynomial samples.Comment: Appeared in FOCS 2017. 55 pages, 1 figur
- …