Martin Lazar

Martin Lazar
University of Dubrovnik · Department of Electrical Engineering and Computing

Professor

About

50
Publications
8,587
Reads
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373
Citations
Introduction
I do research in 1. Control theory: Control of parameter dependent systems (greedy control, averaged control),optimal control of parabolic problems 2. Microlocal analysis: PDEs and homogenisation, velocity averaging, microlocal defect functionals (1-scale H-measures, semiclassical measures, H-distributions) 3. Geophysical fluid dynamics: analytical modelling in oceanography
Additional affiliations
June 2017 - July 2017
University of Deusto
Position
  • Researcher
December 2002 - February 2013
October 2016 - September 2020
University of Dubrovnik
Position
  • CEO

Publications

Publications (50)
Preprint
Full-text available
In this paper we study eigenvalue estimates for the solutions of Lyapunov equations with a noncompact (but relatively Hilbert Schmidt) control operator. We compute eigenvalue estimates from Galerkin discretizations of Lyapunov equations and discuss the appearance of a spurious branch in the discrete spectrum. This phenomenon is called the spectral...
Preprint
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We consider the ensemble controllability problem for a linear time-invariant systeṁ x(t, θ) = A(θ)x(t, θ) + B(θ)u(t), where A and B are continuous matrices with respect to the parameter θ, which belongs to some compact set Θ ⊂ R. Given any continuous initial state datum θ → x 0 (θ) and any continuous target state θ → x 1 (θ), we investigate the num...
Article
Full-text available
We consider parametrized linear-quadratic optimal control problems and provide their online-efficient solutions by combining greedy reduced basis methods and machine learning algorithms. To this end, we first extend the greedy control algorithm, which builds a reduced basis for the manifold of optimal final time adjoint states, to the setting where...
Preprint
Full-text available
Our main contribution in this article is the achievement of the turnpike property in its integral and exponential forms for parameter-dependent systems with averaged observations in the cost functional. Namely, under suitable assumptions with respect to the matrices that defined the dynamics and the cost functional, we prove that the optimal contro...
Article
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Cilj ovog rada je objasniti kako se stvara, razvija i koristi plitka neuronska mreža korištenjem programskog alata MATLAB. Kao testni primjer uzet je problem predviđanja izlaznih vrijednosti rješenja parametarski ovisne diferencijalne jednadžbe prvog reda. Dobiveni rezultati potvrđuju sposobnost neuronske mreže da brzo i pouzdano reproducira tražen...
Article
We show a turnpike result for problems of optimal control with possibly nonlinear systems as well as pointwise-in-time state and control constraints. The objective functional is of integral type and contains a tracking term which penalizes the distance to a desired steady state. In the optimal control problem, only the initial state is prescribed....
Preprint
Full-text available
We consider parametrized linear-quadratic optimal control problems and provide their online-efficient solutions by combining greedy reduced basis methods and machine learning algorithms. To this end, we first extend the greedy control algorithm, which builds a reduced basis for the manifold of optimal final time adjoint states, to the setting where...
Article
Full-text available
The paper provides strong convergence of solutions to a sequence of linear-quadratic (LQ) optimization problems defined in an abstract functional framework. Each problem is accompanied by the constraint of reaching a given target within a prescribed precision. We show that the problems are well-posed and characterize their solutions. The main resul...
Preprint
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This paper is concerned with the eigenvalue decay of solution operators to operator Lyapunov equations, a relevant topic in the context of model reduction for parabolic control problems. We mainly focus on the Gramian operator, which arises in the context of control and observation of heat processes in infinite time, which is normally the first ste...
Preprint
Full-text available
The paper provides strong convergence of solutions to a sequence of linear-quadratic (LQ) optimization problems defined in an abstract functional framework. Each problem is accompanied by the constraint of reaching a given target within a prescribed precision. We show that the problems are well posed and characterise their solutions. The main resul...
Article
The paper investigates switches of circulation orientation in inland basins, either at the surface or near the bottom. The study is based on an analytical 2D model used to simulate thermohaline circulation in lakes and inland seas. The model allows different density profiles varying in both horizontal and vertical directions. By assuming some simpl...
Preprint
Full-text available
We analyse the turnpike properties for a general, infinite dimensional, linear-quadratic (LQ) optimal control problem, both in the deterministic and in the stochastic case. The novelty of the paper is twofold. Firstly, it obtains positive turnpike results for systems that are (partially) uncontrollable. Secondly, it provides turnpike results for av...
Preprint
Full-text available
In this paper we develop a procedure to deal with a family of parameter-dependent ill-posed problems, for which the exact solution in general does not exist. The original problems are relaxed by considering corresponding approximate ones, whose optimal solutions are well defined, where the optimality is determined by the minimal norm requirement. T...
Chapter
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In this chapter we provide an overview of recent progress on the problem of controllability of parameter dependent systems. We explore different control notions successfully developed through the last decade. The aim of the control function is to steer the system to a state satisfying some properties prescribed either at some time instant T>0 or du...
Preprint
Full-text available
The paper investigates switches of circulation orientation in inland basins, either at the surface or near the bottom. The study is based on an analytical 2D model used to simulate thermohaline circulation in lakes and inland seas. The model allows different density profiles varying in both horizontal and vertical directions. By assuming some simpl...
Preprint
Full-text available
In this paper we consider a constrained parabolic optimal control problem. The cost functional is quadratic and it combines the distance of the trajectory of the system from the desired evolution profile together with the cost of a control. The constraint is given by a term measuring the distance between the final state and the desired state toward...
Article
The aim of this paper is to provide an efficient method for solving a family of parameter dependent, algebraic Lyapunov equations in an infinite dimensional setting. Our analysis is based on previous work on reduced modeling and (weak) greedy algorithms for parameter dependent PDEs and abstract equations in Banach spaces. The major contribution is...
Article
Full-text available
We construct an algorithm for solving a constrained optimal control problem for a first-order evolutionary system governed by a positive self-adjoint operator. The problem consists in identifying distributed control that minimizes a given cost functional, which comprises a cost of the control and a trajectory regulation term, while steering the fin...
Preprint
Full-text available
In this chapter we provide an overview of recent progress on the problem of controllability of parameter dependent systems. We explore a different control notions successfully developed through the last decade. The aim of the control function is to steer the system to a state satisfying some properties prescribed either at some time instant T > 0 o...
Preprint
Full-text available
In this article we study a linear control system with unknown parameter. However, we assume that the possible realisations of this parameter are finite and each realisation can appear with a known probability. We aim to design a control independent of the parameter such that the expectation of the system's realisation reach a given target at a fina...
Article
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We extend results obtained by Francfort (An introduction to H-measures and their applications. Variational problems in materials science. Birkhäuser, Basel, pp 85–110, 2006) to parabolic H-measures developed by Antonić and Lazar (J Funct Anal 265:1190–1239, 2013). The well known theory of pseudodifferential operators is extended to parabolic classe...
Article
In this article we consider a linear finite dimensional system. Our aim is to design a control such that the output of the system reach a given target at a final time T>0. This notion is known as output controllability. We extend this notion to the one of long-time output controllability. More precisely, we consider the question: is it possible to...
Preprint
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We extend results obtained by Francfort (2006) to parabolic H-measures developed by Antoni´cAntoni´c and Lazar (2013). The well known theory of pseudodifferential operators is extended to parabolic classes of symbols and operators and used to obtain results applicable to a wide class of partial differential equations. The main result is the propaga...
Article
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In this paper, we deal with the approximation of optimal controls for parameter-dependent elliptic and parabolic equations. We adapt well-known results on greedy algorithms to approximate in an efficient way the optimal controls for parameterized elliptic control problems. Our results yield an optimal approximation procedure that, in particular, pe...
Article
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Practical applications of semiclassical measures are tightly connected with a so called oscillatory property, prevailing leakage of information related to high frequencies. In this paper we propose a complementary, concentratory property which prevents loss of information related to low frequencies. We demonstrate that semiclassical measures attain...
Article
Full-text available
Microlocal defect functionals (H-measures, H-distributions, semiclassical measures etc.) are objects which determine, in some sense, the lack of strong compactness for weakly convergent ${\rm L}^p$ sequences. Recently, Luc Tartar introduced one-scale H-measures, a generalisation of H-measures with a characteristic length, which also comprehend t...
Article
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We prove existence of solutions to Cauchy problem for scalar conservation laws with non-degenerate discontinuous flux $$ \partial_t u+ \hbox{div}f(t,\mathbf{x},u)=s(t,\mathbf{x},u), \quad t\geq 0, \mathbf{x}\in \mathbb{R}^d, $$ where for every $(t,\mathbf{x})\in \mathbb{R}^+\times \mathbb{R}$, the flux $f(t,\mathbf{x},\cdot) \in \hbox{Lip}(\mathbb{...
Article
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We analyse the problem of controllability for parameter-dependent linear finite-dimensional systems. The goal is to identify the most distinguished realisations of those parameters so to better describe or approximate the whole range of controls. We adapt recent results on greedy and weak greedy algorithms for parameter depending PDEs or, more gene...
Article
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A method is developed for analysing asymptotic behaviour of terms involving an arbitrary integer order powers of L p functions by means of H-measures. It is applied to the small amplitude homogenisation problem for a stationary diffusion equation, in which coefficients are assumed to be analytic perturbations of a constant, enabling formulæ for hig...
Article
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This paper deals with an optimal control problem of Bolza type for a class of parabolic equations. It consists in �nding the initial datum that minimises a cost functional, which comprises an energy term on the control and a regulation term given by a distributed cost on the state, and such that the �nal state lies within a prescribed distance to a...
Article
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We introduce a new family of functional spaces which incorporate Bochner spaces L p (R m ; E), with E being an appropriate Banach space, and to which we extend the H-distributions. We use the developed theory to prove a general version of the velocity averaging lemma in a heterogeneous L p , p ≤ 2 setting.
Article
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We analyse stability of observability estimates for solutions to wave and Scr\" odinger equations subjected to additive perturbations. The paper generalises the recent averaged observability/control result by allowing for systems consisting of operators of different types. The method also applies to the simultaneous observability problem by which o...
Article
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We analyze the problem of averaged observability and control of wave equations. This topic is motivated by the control of parameter-dependent systems of wave equations. We look for controls ensuring the controllability of the averages of the states with respect to the parameter. This turns out to be equivalent to the problem of averaged observati...
Article
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Assume that $(u_n)$ is a sequence of solutions to equations with fractional derivatives, weakly converging to zero in ${\rm L}^p(R^{d+m})$, with $p\leq 2$. We prove that the sequence of averaged quantities $(\int \rho(y) u_n(x,y) dy)$ is strongly precompact in $L^1_{loc}(R^d)$ for any $\rho\in C_c{\R^m}$, provided that restrictive non-degeneracy co...
Article
Classical H-measures introduced by L. Tartar [Proc. R. Soc. Edinb., Sect. A, Math. 115, No. 3–4, 193–230 (1990; Zbl 0774.35008)] and independently by P. Gérard [Commun. Partial Differ. Equations 16, No. 11, 1761–1794 (1991; Zbl 0770.35001)] are not well suited for the study of parabolic equations. Recently, several parabolic variants have been prop...
Article
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We examine necessary and sufficient conditions under which a continuous bilinear functional B on Lp(Rd)⊗ELp(Rd)⊗E, p>1p>1, E being a separable Banach space, can be continuously extended to a linear functional on Lp(Rd;E)Lp(Rd;E). The extension enables a generalisation of the H-distribution concept, allowing us to obtain a (heterogeneous) velocity a...
Article
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We prove that the sequence of averaged quantities $\int_{\R^m}u_n(\mx,\msnop)$ $\rho(\msnop)d\msnop$, is strongly precompact in $\Ldl\Rd$, where $\rho\in \Ldc{\R^m}$, and $u_n\in \Ld{\R^m; \pL s\Rd}$, $s\geq 2$, are weak solutions to differential operator equations with variable coefficients. In particular, this includes differential operators of h...
Article
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We prove that the sequence of averaged quantities ∫Rm un(t,x,y)v(y)dy is strongly precompact in L2loc(R1+d), where u ε L2c (Rm), and un ε L2(R1+d x Rm) are solutions to strictly parabolic transport equations with flux explicitly depending on space and time. In order to obtain the result, we use a recently introduced parabolic variant of H-measures.
Article
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H-measures, as originally introduced by Luc Tartar and (independently) Patrick Gérard are well suited for hyperbolic problems. For parabolic problems, some variants should be considered, which would be better adapted to parabolic problems.Recently, we introduced a few parabolic scalings and corresponding variant H-measures, including the existence...
Article
Full-text available
A simple diagnostic model, reproducing circulation in lakes and marginal seas in which low-density waters are found close to the coasts while high-density waters dominate the offshore areas, is developed. An explicit solution is obtained for the central transverse section of an elongated basin, assuming that the Boussinesq and hydrostatic approxima...
Article
Full-text available
H-measures, as originally introduced by Luc Tartar and Patrick Gérard, are suited to hyperbolic problems. However, they turned out not to be well adjusted to the study of parabolic equations. A variant of H-measures is proposed, which is much better adapted to such kind of problems. We present the new parabolic scaling and the main ingredients for...
Article
A new, parabolic variant of H-measures, as well as its application to the advection-diffusion equation is presented. By the means of localisation property, the strong compactness for gradients of solutions is obtained in the case of variable coefficients. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Article
Since their introduction H-measures have been mostly used in problems related to propagation effects for hyperbolic equations and systems. In this study we give an attempt to apply the H-measure theory to other types of equations. Through a number of examples we present how do the differences between parabolic and hyperbolic equations reflect in th...
Article
Two diagnostic models, reproducing circulation generated in a marginal sea by variable density, have been developed. The models’ domain is a 2D transverse section for which analytical solutions have been obtained. They describe the winter situation in the northern Adriatic, with a strong vertical mixing present and the density maximum dominating th...
Article
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Starting from the method for computing microlocal energy density, which was developed independently by Francfort and Murat, and Gérard for the linear wave equation, we compute that very density for the hyperbolic system We express the energy limit for the sequence of initial problems in terms of the energy of initial conditions. The basic tool we u...
Article
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In the theory of homogenisation it is of particular interest to determine the classes of problems which are stable on taking the homogenisation limit. A notable situation where the limit enlarges the class of original problems is known as memory (nonlocal) effects. A number of results in that direction has been obtained for linear problems. Tartar...

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