Stability and Recovery for Independence Systems

Two genres of heuristics that are frequently reported to perform much better on "real-world" instances than in the worst case are greedy algorithms and local search algorithms. In this paper, we systematically study these two types of algorithms for the problem of maximizing a monotone submodular set function subject to downward-closed feasibility constraints. We consider perturbation-stable instances, in the sense of Bilu and Linial [11], and precisely identify the stability threshold beyond which these algorithms are guaranteed to recover the optimal solution. Byproducts of our work include the first definition of perturbation-stability for non-additive objective functions, and a resolution of the worst-case approximation guarantee of local search in p-extendible systems

Graphical continuous Lyapunov models

The linear Lyapunov equation of a covariance matrix parametrizes the equilibrium covariance matrix of a stochastic process. This parametrization can be interpreted as a new graphical model class, and we show how the model class behaves under marginalization and introduce a method for structure learning via $\ell_1$-penalized loss minimization. Our proposed method is demonstrated to outperform alternative structure learning algorithms in a simulation study, and we illustrate its application for protein phosphorylation network reconstruction.Comment: 10 pages, 5 figure

Bridging the computational gap between mesoscopic and continuum modeling of red blood cells for fully resolved blood flow

We present a computational framework for the simulation of blood flow with fully resolved red blood cells (RBCs) using a modular approach that consists of a lattice Boltzmann solver for the blood plasma, a novel finite element based solver for the deformable bodies and an immersed boundary method for the fluid-solid interaction. For the RBCs, we propose a nodal projective FEM (npFEM) solver which has theoretical advantages over the more commonly used mass-spring systems (mesoscopic modeling), such as an unconditional stability, versatile material expressivity, and one set of parameters to fully describe the behavior of the body at any mesh resolution. At the same time, the method is substantially faster than other FEM solvers proposed in this field, and has an efficiency that is comparable to the one of mesoscopic models. At its core, the solver uses specially defined potential energies, and builds upon them a fast iterative procedure based on quasi-Newton techniques. For a known material, our solver has only one free parameter that demands tuning, related to the body viscoelasticity. In contrast, state-of-the-art solvers for deformable bodies have more free parameters, and the calibration of the models demands special assumptions regarding the mesh topology, which restrict their generality and mesh independence. We propose as well a modification to the potential energy proposed by Skalak et al. 1973 for the red blood cell membrane, which enhances the strain hardening behavior at higher deformations. Our viscoelastic model for the red blood cell, while simple enough and applicable to any kind of solver as a post-convergence step, can capture accurately the characteristic recovery time and tank-treading frequencies. The framework is validated using experimental data, and it proves to be scalable for multiple deformable bodies

Central Bank’s Role and Involvement in Bank Regulation: Lender of Last Resort Arrangements and the Special Resolution Regime (SRR)

This paper considers developments which have necessitated greater involvement and a greater role for the central bank in financial regulation and supervision. The aftermath of the 2007/08 Financial Crisis has witnessed the enactment of legislation such as the Banking Act of 2009 which has not only introduced greater statutory powers for the central bank, but also the Special Resolution Regime. As well as a consideration of arguments which are in favour of the central bank’s role as supervisor and lender of last resort, the importance of central bank independence and safeguards which exist to ensure that sufficient accountability is fostered, will be considered. Safeguards and accountability mechanisms which are adequate, such that, whilst ensuring that the regulator is not susceptible to regulatory capture, do not impede the ability of such a regulator to obtain vital and necessary information from systemically important individual financial institutions. In its support of the view that central banks should assume a greater role in supervision, this paper not only seeks to justify why such a degree of involvement is vital to ensuring and maintaining stability in the financial system, but also those factors which are considered to be necessary if such a role is to be effectiv

Signal Recovery From Random Measurements Via Orthogonal Matching Pursuit

This paper demonstrates theoretically and empirically that a greedy algorithm called Orthogonal Matching Pursuit (OMP) can reliably recover a signal with $m$ nonzero entries in dimension $d$ given ${rm O}(m ln d)$ random linear measurements of that signal. This is a massive improvement over previous results, which require ${rm O}(m^{2})$ measurements. The new results for OMP are comparable with recent results for another approach called Basis Pursuit (BP). In some settings, the OMP algorithm is faster and easier to implement, so it is an attractive alternative to BP for signal recovery problems

Administrative review mechanisms within the ECB

The single supervisory mechanism and the single resolution mechanism are the two main pillars of the European banking union. These complex frameworks encompass innovative quasi-judicial systems which allow undertakings and national authorities to contend certain decisions taken respectively by the ECB and the SRB, through two technical independent bodies, namely an Administrative Board of Review (ABoR) and an Appeal Panel. Through a comparison of the founding provisions of these two panels with other similar experiences in highly regulated technical sectors, it is argued that the current architecture of nonjudicial remedies available in the banking union is not set up as a single unitary model, but as an hybrid one with distinctive features adapted to the peculiarities of supervisory and recovery functions. It is questionable whether such characteristic may impair the position of private individuals and the ability to cope with the complex matters concerned in an effective way