Bidirected minimum Manhattan network problem

In the bidirected minimum Manhattan network problem, given a set T of n terminals in the plane, we need to construct a network N(T) of minimum total length with the property that the edges of N(T) are axis-parallel and oriented in a such a way that every ordered pair of terminals is connected in N(T) by a directed Manhattan path. In this paper, we present a polynomial factor 2 approximation algorithm for the bidirected minimum Manhattan network problem.Comment: 14 pages, 16 figure

Certifying cost annotations in compilers

We discuss the problem of building a compiler which can lift in a provably correct way pieces of information on the execution cost of the object code to cost annotations on the source code. To this end, we need a clear and flexible picture of: (i) the meaning of cost annotations, (ii) the method to prove them sound and precise, and (iii) the way such proofs can be composed. We propose a so-called labelling approach to these three questions. As a first step, we examine its application to a toy compiler. This formal study suggests that the labelling approach has good compositionality and scalability properties. In order to provide further evidence for this claim, we report our successful experience in implementing and testing the labelling approach on top of a prototype compiler written in OCAML for (a large fragment of) the C language

Feedback control and optimization for the production of commercial fuels by blending

International audienceThis paper presents a control algorithm for blending systems. Such systems are used in refining to produce mixtures having specified properties from several components. The underlying control problem is multi-variable, with constraints on the inputs and outputs, and involves large uncertainties. To address this complexity, a constrained optimization problem is formulated, while the uncertainties are treated in closed-loop by an estimator of the components properties. Besides a theoretical study of the main algorithm and a study of convergence, the paper presents numerous technical details that are needed to solve blending problems as they appear in refining operations. Among them are a general lack of measurements, variable delays, measurement synchronization, infeasibilities management, hydraulic constraints, and pre-blends. Industrial case-studies are provided and stress the relevance of the approach