Artikel in Referierten Journalen

  • A. Alphonse, M. Hintermüller, C.N. Rautenberg, Directional differentiability for elliptic quasi-variational inequalities of obstacle type, Calculus of Variations and Partial Differential Equations, (2019), published online on 24.01.2019, DOI 10.1007/s00526-018-1473-0 .
    The directional differentiability of the solution map of obstacle type quasi-variational inequal- ities (QVIs) with respect to perturbations on the forcing term is studied. The classical result of Mignot is then extended to the quasi-variational case under assumptions that allow multiple solu- tions of the QVI. The proof involves selection procedures for the solution set and represents the directional derivative as the limit of a monotonic sequence of directional derivatives associated to specific variational inequalities. Additionally, estimates on the coincidence set and several sim- plifications under higher regularity are studied. The theory is illustrated by a detailed study of an application to thermoforming comprising of modelling, analysis and some numerical experiments.

  • L. Adam, M. Hintermüller, D. Peschka, Th.M. Surowiec, Optimization of a multiphysics problem in semiconductor laser design, SIAM Journal on Applied Mathematics, 79 (2019), pp. 257--283, DOI 10.1137/18M1179183 .
    A multimaterial topology optimization framework is suggested for the simultaneous optimization of mechanical and optical properties to be used in the development of optoelectronic devices. Based on the physical aspects of the underlying device, a nonlinear multiphysics model for the elastic and optical properties is proposed. Rigorous proofs are provided for the sensitivity of the fundamental mode of the device with respect to the changes in the underlying topology. After proving existence and optimality results, numerical experiments leading to an optimal material distribution for maximizing the strain in a Ge-on-Si microbridge are given. The highly favorable electronic properties of this design are demonstrated by steady-state simulations of the corresponding van Roosbroeck (drift-diffusion) system.

  • G. Dong, M. Hintermüller, K. Papafitsoros, Quantitative magnetic resonance imaging: from fingerprinting to integrated physics--based models, SIAM Journal on Imaging Sciences, 2 (2019), pp. 927-971, DOI 10.1137/18M1222211 .
    Quantitative magnetic resonance imaging (qMRI) is concerned with estimating (in physical units) values of magnetic and tissue parameters, e.g., relaxation times $T_1$, $T_2$, or proton density $rho$. Recently, in [Ma et al., Nature, 495 (2013), pp. 187--193], magnetic resonance fingerprinting (MRF) was introduced as a technique being capable of simultaneously recovering such quantitative parameters by using a two-step procedure: (i) given a probe, a series of magnetization maps are computed and then (ii) matched to (quantitative) parameters with the help of a precomputed dictionary which is related to the Bloch manifold. In this paper, we first put MRF and its variants into perspective with optimization and inverse problems to gain mathematical insights concerning identifiability of parameters under noise and interpretation in terms of optimizers. Motivated by the fact that the Bloch manifold is nonconvex and that the accuracy of the MRF-type algorithms is limited by the ?discretization size? of the dictionary, a novel physics-based method for qMRI is proposed. In contrast to the conventional two-step method, our model is dictionary-free and is rather governed by a single nonlinear equation, which is studied analytically. This nonlinear equation is efficiently solved via robustified Newton-type methods. The effectiveness of the new method for noisy and undersampled data is shown both analytically and via extensive numerical examples, for which improvement over MRF and its variants is also documented.

  • A. Alphonse, Ch.M. Elliott, J. Terra, A coupled ligand-receptor bulk-surface system on a moving domain: Well posedness, regularity and convergence to equilibrium, SIAM Journal on Mathematical Analysis, 50 (2018), pp. 1544--1592, DOI 10.1137/16M110808X .
    We prove existence, uniqueness, and regularity for a reaction-diffusion system of coupled bulk-surface equations on a moving domain modelling receptor-ligand dynamics in cells. The nonlinear coupling between the three unknowns is through the Robin boundary condition for the bulk quantity and the right hand sides of the two surface equations. Our results are new even in the non-moving setting, and in this case we also show exponential convergence to a steady state. The primary complications in the analysis are indeed the nonlinear coupling and the Robin boundary condition. For the well posedness and essential boundedness of solutions we use several De Giorgi-type arguments, and we also develop some useful estimates to allow us to apply a Steklov averaging technique for time-dependent operators to prove that solutions are strong. Some of these auxiliary results presented in this paper are of independent interest by themselves.

  • A. Ceretani, C.N. Rautenberg, The Boussinesq system with mixed non-smooth boundary conditions and ``do-nothing'' boundary flow, Zeitschrift fur Angewandte Mathematik und Physik. ZAMP. Journal of Applied Mathematics and Physics. Journal de Mathematiques et de Physique Appliquees, 70 (2019), pp. 14/1--14/24 (published online on 07.12.2018), DOI 10.1007/s00033-018-1058-y .
    A stationary Boussinesq system for an incompressible viscous fluid in a bounded domain with a nontrivial condition at an open boundary is studied. We consider a novel non-smooth boundary condition associated to the heat transfer on the open boundary that involves the temperature at the boundary, the velocity of the fluid, and the outside temperature. We show that this condition is compatible with two approaches at dealing with the do-nothing boundary condition for the fluid: 1) the directional do-nothing condition and 2) the do-nothing condition together with an integral bound for the backflow. Well-posedness of variational formulations is proved for each problem.

  • L. Adam, M. Hintermüller, Th.M. Surowiec, A PDE-constrained optimization approach for topology optimization of strained photonic devices, Annali di Matematica Pura ed Applicata. Serie Quarta. Fondazione Annali di Matematica Pura ed Applicata, c/o Dipartimento di Matematica ``U. Dini'', Firenze; Springer-Verlag, Heidelberg. English, French, German, Italian, English abstracts., 19 (2018), pp. 521--557, DOI 10.1007/s11081-018-9394-5 .
    Recent studies have demonstrated the potential of using tensile-strained, doped Germanium as a means of developing an integrated light source for (amongst other things) future microprocessors. In this work, a multi-material phase-field approach to determine the optimal material configuration within a so-called Germanium-on-Silicon microbridge is considered. Here, an “optimal" configuration is one in which the strain in a predetermined minimal optical cavity within the Germanium is maximized according to an appropriately chosen objective functional. Due to manufacturing requirements, the emphasis here is on the cross-section of the device; i.e. a socalled aperture design. Here, the optimization is modeled as a non-linear optimization problem with partial differential equation (PDE) and manufacturing constraints. The resulting problem is analyzed and solved numerically. The theory portion includes a proof of existence of an optimal topology, differential sensitivity analysis of the displacement with respect to the topology, and the derivation of first and second-order optimality conditions. For the numerical experiments, an array of first and second-order solution algorithms in function-space are adapted to the current setting, tested, and compared. The numerical examples yield designs for which a significant increase in strain (as compared to an intuitive empirical design) is observed.

  • L. Adam, M. Hintermüller, Th.M. Surowiec, A semismooth Newton method with analytical path-following for the $H^1$-projection onto the Gibbs simplex, IMA Journal of Numerical Analysis, published online on 07.06.2018, DOI 10.1093/imanum/dry034 .
    An efficient, function-space-based second-order method for the $H^1$-projection onto the Gibbs-simplex is presented. The method makes use of the theory of semismooth Newton methods in function spaces as well as Moreau-Yosida regularization and techniques from parametric optimization. A path-following technique is considered for the regularization parameter updates. A rigorous first and second-order sensitivity analysis of the value function for the regularized problem is provided to justify the update scheme. The viability of the algorithm is then demonstrated for two applications found in the literature: binary image inpainting and labeled data classification. In both cases, the algorithm exhibits mesh-independent behavior.

  • H. Antil, C.N. Rautenberg, Fractional elliptic quasi-variational inequalities: Theory and numerics, Interfaces and Free Boundaries. Mathematical Modelling, Analysis and Computation, 20 (2018), pp. 1--24, DOI 10.4171/IFB/395 .

  • M. Hintermüller, M. Hinze, Ch. Kahle, T. Keil, A goal-oriented dual-weighted adaptive finite element approach for the optimal control of a nonsmooth Cahn--Hilliard--Navier--Stokes system, Optimization and Engineering. International Multidisciplinary Journal to Promote Optimization Theory & Applications in Engineering Sciences, 19 (2018), pp. 629--662, DOI 10.1007/s11081-018-9393-6 .
    This paper is concerned with the development and implementation of an adaptive solution algorithm for the optimal control of a time-discrete Cahn--Hilliard--Navier--Stokes system with variable densities. The free energy density associated to the Cahn--Hilliard system incorporates the double-obstacle potential which yields an optimal control problem for a family of coupled systems in each time instant of a variational inequality of fourth order and the Navier--Stokes equation. A dual-weighed residual approach for goal-oriented adaptive finite elements is presented which is based on the concept of C-stationarity. The overall error representation depends on primal residual weighted by approximate dual quantities and vice versa as well as various complementary mismatch errors. Details on the numerical realization of the adaptive concept and a report on numerical tests are given.

  • M. Hintermüller, M. Holler, K. Papafitsoros, A function space framework for structural total variation regularization with applications in inverse problems, Inverse Problems. An International Journal on the Theory and Practice of Inverse Problems, Inverse Methods and Computerized Inversion of Data, 34 (2018), pp. 064002/1--064002/39, DOI 10.1088/1361-6420/aab586 .
    In this work, we introduce a function space setting for a wide class of structural/weighted total variation (TV) regularization methods motivated by their applications in inverse problems. In particular, we consider a regularizer that is the appropriate lower semi-continuous envelope (relaxation) of a suitable total variation type functional initially defined for sufficiently smooth functions. We study examples where this relaxation can be expressed explicitly, and we also provide refinements for weighted total variation for a wide range of weights. Since an integral characterization of the relaxation in function space is, in general, not always available, we show that, for a rather general linear inverse problems setting, instead of the classical Tikhonov regularization problem, one can equivalently solve a saddle-point problem where no a priori knowledge of an explicit formulation of the structural TV functional is needed. In particular, motivated by concrete applications, we deduce corresponding results for linear inverse problems with norm and Poisson log-likelihood data discrepancy terms. Finally, we provide proof-of-concept numerical examples where we solve the saddle-point problem for weighted TV denoising as well as for MR guided PET image reconstruction.

  • M. Hintermüller, C.N. Rautenberg, N. Strogies, Dissipative and non-dissipative evolutionary quasi-variational inequalities with gradient constraints, Set-Valued and Variational Analysis. Theory and Applications. Springer, Dordrecht. English., pp. published online on 14.07.2018, url, DOI 10.1007/s11228-018-0489-0 .
    Evolutionary quasi-variational inequality (QVI) problems of dissipative and non-dissipative nature with pointwise constraints on the gradient are studied. A semi-discretization in time is employed for the study of the problems and the derivation of a numerical solution scheme, respectively. Convergence of the discretization procedure is proven and properties of the original infinite dimensional problem, such as existence, extra regularity and non-decrease in time, are derived. The proposed numerical solver reduces to a finite number of gradient-constrained convex optimization problems which can be solved rather efficiently. The paper ends with a report on numerical tests obtained by a variable splitting algorithm involving different nonlinearities and types of constraints.

Beiträge zu Sammelwerken

  • M. Hintermüller, T. Keil, Some recent developments in optimal control of multiphase flows, in: Shape Optimization, Homogenization and Optimal Control. DFG-AIMS Workshop held at the AIMS Center Senegal, March 13--16, 2017, V. Schulz, D. Seck, eds., 169 of International Series of Numerical Mathematics, Birkhäuser, Springer Nature Switzerland AG, Cham, 2018, pp. 113--142, DOI 10.1007/978-3-319-90469-6_7 .

  • M. Hintermüller, A. Langer, C.N. Rautenberg, T. Wu, Adaptive regularization for image reconstruction from subsampled data, in: Imaging, Vision and Learning Based on Optimization and PDEs IVLOPDE, Bergen, Norway, August 29 -- September 2, 2016, X.-Ch. Tai, E. Bae, M. Lysaker, eds., Mathematics and Visualization, Springer International Publishing, Berlin, 2018, pp. 3--26, DOI 10.1007/978-3-319-91274-5 .
    Choices of regularization parameters are central to variational methods for image restoration. In this paper, a spatially adaptive (or distributed) regularization scheme is developed based on localized residuals, which properly balances the regularization weight between regions containing image details and homogeneous regions. Surrogate iterative methods are employed to handle given subsampled data in transformed domains, such as Fourier or wavelet data. In this respect, this work extends the spatially variant regularization technique previously established in [15], which depends on the fact that the given data are degraded images only. Numerical experiments for the reconstruction from partial Fourier data and for wavelet inpainting prove the efficiency of the newly proposed approach.

Preprints, Reports, Technical Reports

  • C. Grässle, M. Hintermüller, M. Hinze, T. Keil, Simulation and control of a nonsmooth Cahn--Hilliard Navier--Stokes system with variable fluid densities, Preprint no. 2617, WIAS, Berlin, 2019, DOI 10.20347/WIAS.PREPRINT.2617 .
    Abstract, PDF (11 MByte)
    We are concerned with the simulation and control of a two phase flow model governed by a coupled Cahn--Hilliard Navier--Stokes system involving a nonsmooth energy potential.We establish the existence of optimal solutions and present two distinct approaches to derive suitable stationarity conditions for the bilevel problem, namely C- and strong stationarity. Moreover, we demonstrate the numerical realization of these concepts at the hands of two adaptive solution algorithms relying on a specifically developed goal-oriented error estimator.In addition, we present a model order reduction approach using proper orthogonal decomposition (POD-MOR) in order to replace high-fidelity models by low order surrogates. In particular, we combine POD with space-adapted snapshots and address the challenges which are the consideration of snapshots with different spatial resolutions and the conservation of a solenoidal property.

  • M. Hintermüller, T. Keil, Optimal control of geometric partial differential equations, Preprint no. 2612, WIAS, Berlin, 2019, DOI 10.20347/WIAS.PREPRINT.2612 .
    Abstract, PDF (15 MByte)
    Optimal control problems for geometric (evolutionary) partial differential inclusions are considered. The focus is on problems which, in addition to the nonlinearity due to geometric evolution, contain optimization theoretic challenges because of non-smoothness. The latter might stem from energies containing non-smooth constituents such as obstacle-type potentials or terms modeling, e.g., pinning phenomena in microfluidics. Several techniques to remedy the resulting constraint degeneracy when deriving stationarity conditions are presented. A particular focus is on Yosida-type mollifications approximating the original degenerate problem by a sequence of nondegenerate nonconvex optimal control problems. This technique is also the starting point for the development of numerical solution schemes. In this context, also dual-weighted residual based error estimates are addressed to facilitate an adaptive mesh refinement. Concerning the underlying state model, sharp and diffuse interface formulations are discussed. While the former always allows for accurately tracing interfacial motion, the latter model may be dictated by the underlying physical phenomenon, where near the interface mixed phases may exist, but it may also be used as an approximate model for (sharp) interface motion. In view of the latter, (sharp interface) limits of diffuse interface models are addressed. For the sake of presentation, this exposition confines itself to phase field type diffuse interface models and, moreover, develops the optimal control of either of the two interface models along model applications. More precisely, electro-wetting on dielectric is used in the sharp interface context, and the control of multiphase fluids involving spinodal decomposition highlights the phase field technique. Mathematically, the former leads to a Hele-Shaw flow with geometric boundary conditions involving a complementarity system due to contact line pinning, and the latter gives rise to a Cahn-Hilliard Navier-Stokes model including a non-smooth obstacle type potential leading to a variational inequality constraint.

  • M. Hintermüller, K. Papafitsoros, Generating structured non-smooth priors and associated primal-dual methods, Preprint no. 2611, WIAS, Berlin, 2019, DOI 10.20347/WIAS.PREPRINT.2611 .
    Abstract, PDF (22 MByte)
    The purpose of the present chapter is to bind together and extend some recent developments regarding data-driven non-smooth regularization techniques in image processing through the means of a bilevel minimization scheme. The scheme, considered in function space, takes advantage of a dualization framework and it is designed to produce spatially varying regularization parameters adapted to the data for well-known regularizers, e.g. Total Variation and Total Generalized variation, leading to automated (monolithic), image reconstruction workflows. An inclusion of the theory of bilevel optimization and the theoretical background of the dualization framework, as well as a brief review of the aforementioned regularizers and their parameterization, makes this chapter a self-contained one. Aspects of the numerical implementation of the scheme are discussed and numerical examples are provided.

  • A. Alphonse, M. Hintermüller, C.N. Rautenberg, Existence, iteration procedures and directional differentiability for parabolic QVIs, Preprint no. 2592, WIAS, Berlin, 2019, DOI 10.20347/WIAS.PREPRINT.2592 .
    Abstract, PDF (408 kByte)
    We study parabolic quasi-variational inequalities (QVIs) of obstacle type. Under appropriate assumptions on the obstacle mapping, we prove the existence of solutions of such QVIs by two methods: one by time discretisation through elliptic QVIs and the second by iteration through parabolic variational inequalities (VIs). Using these results, we show the directional differentiability (in a certain sense) of the solution map which takes the source term of a parabolic QVI into the set of solutions, and we relate this result to the contingent derivative of the aforementioned map. We finish with an example where the obstacle mapping is given by the inverse of a parabolic differential operator.

  • G. Dong, M. Hintermüller, Y. Zhang, A class of second-order geometric quasilinear hyperbolic PDEs and their application in imaging science, Preprint no. 2591, WIAS, Berlin, 2019, DOI 10.20347/WIAS.PREPRINT.2591 .
    Abstract, PDF (1181 kByte)
    In this paper, we study damped second-order dynamics, which are quasilinear hyperbolic partial differential equations (PDEs). This is inspired by the recent development of second-order damping systems for accelerating energy decay of gradient flows. We concentrate on two equations: one is a damped second-order total variation flow, which is primarily motivated by the application of image denoising; the other is a damped second-order mean curvature flow for level sets of scalar functions, which is related to a non-convex variational model capable of correcting displacement errors in image data (e.g. dejittering). For the former equation, we prove the existence and uniqueness of the solution. For the latter, we draw a connection between the equation and some second-order geometric PDEs evolving the hypersurfaces which are described by level sets of scalar functions, and show the existence and uniqueness of the solution for a regularized version of the equation. The latter is used in our algorithmic development. A general algorithm for numerical discretization of the two nonlinear PDEs is proposed and analyzed. Its efficiency is demonstrated by various numerical examples, where simulations on the behavior of solutions of the new equations and comparisons with first-order flows are also documented.

  • A. Alphonse, M. Hintermüller, C.N. Rautenberg, Stability of the solution set of quasi-variational inequalities and optimal control, Preprint no. 2582, WIAS, Berlin, 2019, DOI 10.20347/WIAS.PREPRINT.2582 .
    Abstract, PDF (321 kByte)
    For a class of quasivariational inequalities (QVIs) of obstacle-type the stability of its solution set and associated optimal control problems are considered. These optimal control problems are non-standard in the sense that they involve an objective with set-valued arguments. The approach to study the solution stability is based on perturbations of minimal and maximal elements to the solution set of the QVI with respect to monotonic perturbations of the forcing term. It is shown that different assumptions are required for studying decreasing and increasing perturbations and that the optimization problem of interest is well-posed.

  • L. Calatroni, K. Papafitsoros, Analysis and optimisation of a variational model for mixed Gaussian and Salt & Pepper noise removal, Preprint no. 2542, WIAS, Berlin, 2018, DOI 10.20347/WIAS.PREPRINT.2542 .
    Abstract, PDF (946 kByte)
    We analyse a variational regularisation problem for mixed noise removal that was recently proposed in [14]. The data discrepancy term of the model combines L1 and L2 terms in an infimal convolution fashion and it is appropriate for the joint removal of Gaussian and Salt & Pepper noise. In this work we perform a finer analysis of the model which emphasises on the balancing effect of the two parameters appearing in the discrepancy term. Namely, we study the asymptotic behaviour of the model for large and small values of these parameters and we compare it to the corresponding variational models with L1 and L2 data fidelity. Furthermore, we compute exact solutions for simple data functions taking the total variation as regulariser. Using these theoretical results, we then analytically study a bilevel optimisation strategy for automatically selecting the parameters of the model by means of a training set. Finally, we report some numerical results on the selection of the optimal noise model via such strategy which confirm the validity of our analysis and the use of popular data models in the case of "blind” model selection.

  • S. Hajian, M. Hintermüller, C. Schillings, N. Strogies, A Bayesian approach to parameter identification in gas networks, Preprint no. 2537, WIAS, Berlin, 2018, DOI 10.20347/WIAS.PREPRINT.2537 .
    Abstract, PDF (505 kByte)
    The inverse problem of identifying the friction coefficient in an isothermal semilinear Euler system is considered. Adopting a Bayesian approach, the goal is to identify the distribution of the quantity of interest based on a finite number of noisy measurements of the pressure at the boundaries of the domain. First well-posedness of the underlying non-linear PDE system is shown using semigroup theory, and then Lipschitz continuity of the solution operator with respect to the friction coefficient is established. Based on the Lipschitz property, well-posedness of the resulting Bayesian inverse problem for the identification of the friction coefficient is inferred. Numerical tests for scalar and distributed parameters are performed to validate the theoretical results.

  • J. Polzehl, K. Papafitsoros, K. Tabelow, Patch-wise adaptive weights smoothing, Preprint no. 2520, WIAS, Berlin, 2018, DOI 10.20347/WIAS.PREPRINT.2520 .
    Abstract, PDF (28 MByte)
    Image reconstruction from noisy data has a long history of methodological development and is based on a variety of ideas. In this paper we introduce a new method called patch-wise adaptive smoothing, that extends the Propagation-Separation approach by using comparisons of local patches of image intensities to define local adaptive weighting schemes for an improved balance of reduced variability and bias in the reconstruction result. We present the implementation of the new method in an R package aws and demonstrate its properties on a number of examples in comparison with other state-of-the art image reconstruction methods.

  • A. Alphonse, M. Hintermüller, C.N. Rautenberg, Recent trends and views on elliptic quasi-variational inequalities, Preprint no. 2518, WIAS, Berlin, 2018, DOI 10.20347/WIAS.PREPRINT.2518 .
    Abstract, PDF (452 kByte)
    We consider state-of-the-art methods, theoretical limitations, and open problems in elliptic Quasi-Variational Inequalities (QVIs). This involves the development of solution algorithms in function space, existence theory, and the study of optimization problems with QVI constraints. We address the range of applicability and theoretical limitations of fixed point and other popular solution algorithms, also based on the nature of the constraint, e.g., obstacle and gradient-type. For optimization problems with QVI constraints, we study novel formulations that capture the multivalued nature of the solution mapping to the QVI, and generalized differentiability concepts appropriate for such problems.

  • H. Antil, C.N. Rautenberg, Sobolev spaces with non-Muckenhoupt weights, fractional elliptic operators, and applications, Preprint no. 2505, WIAS, Berlin, 2018, DOI 10.20347/WIAS.PREPRINT.2505 .
    Abstract, PDF (7959 kByte)
    We propose a new variational model in weighted Sobolev spaces with non-standard weights and applications to image processing. We show that these weights are, in general, not of Muckenhoupt type and therefore the classical analysis tools may not apply. For special cases of the weights, the resulting variational problem is known to be equivalent to the fractional Poisson problem. The trace space for the weighted Sobolev space is identified to be embedded in a weighted L2 space. We propose a finite element scheme to solve the Euler-Lagrange equations, and for the image denoising application we propose an algorithm to identify the unknown weights. The approach is illustrated on several test problems and it yields better results when compared to the existing total variation techniques.

Vorträge, Poster

  • A. Alphonse, Directional differentiability for elliptic quasi-variational inequalities, Workshop ``Surface, Bulk, and Geometric Partial Differential Equations: Interfacial, stochastic, non-local and discrete structures'', January 20 - 26, 2019, Mathematisches Forschungsinstitut Oberwolfach, January 25, 2019.

  • A. Alphonse, Directional differentiability for elliptic quasi-variational inequalities, ICCOPT 2019, August 5 - 8, 2019, WIAS - FU Berlin - HU Berlin - TU Berlin, January 6, 2019.

  • M. Hintermüller, (Pre)Dualization, dense embeddings of convex sets, and applications in image processing, Thematic Programme ``Modern Maximal Monotone Operator Theory: From Nonsmooth Optimization to Differential Inclusions'', Workshop ``Numerical Algorithms in Nonsmooth Optimization'', February 25 - March 1, 2019, Erwin Schrödinger International Institute for Mathematics and Physics, Vienna, Austria, February 28, 2019.

  • M. Hintermüller, A function space framework for structural total variation regularization with applications in inverse problems, 71st Workshop: Advances in Nonsmooth Analysis and Optimization (NAO2019), June 25 - 30, 2019, International School of Mathematics ``Guido Stampacchia'', Erice, Italy, June 26, 2019.

  • M. Hintermüller, A function space framework for structural total variation regularization with applications in inverse problems, Thematic Programme ``Modern Maximal Monotone Operator Theory: From Nonsmooth Optimization to Differential Inclusions'', Workshop ``Nonsmooth and Variational Analysis'', January 28 - February 1, 2019, Erwin Schrödinger International Institute for Mathematics and Physics, Vienna, Austria, February 1, 2019.

  • M. Hintermüller, A physically oriented method for quantitative magnetic resonance imaging, 9th International Congress on Industrial and Applied Mathematics (ICIAM 2019), Session MS A1-1-3 5: ``Computationally Efficient Methods for Large-scale Inverse Problems in Imaging Applications'', July 15 - 19, 2019, Valencia, Spain, July 17, 2019.

  • M. Hintermüller, Applications in image processing, Workshop on Efficient Operator Splitting Techniques for Complex System and Large Scale Data Analysis, January 15 - 18, 2019, Sanya, China, January 14, 2019.

  • M. Hintermüller, Generalized Nash equilibrium problems with PDEs connected to spot markets with (gas) transport, 9th International Congress on Industrial and Applied Mathematics (ICIAM 2019), Session MS ME-1-4 1: ``Recent Advances in PDE-constrained Optimization'', July 15 - 19, 2019, Valencia, Spain, July 15, 2019.

  • M. Hintermüller, Generalized Nash equilibrium problems with application to spot markets with gas transport, Workshop ``Electricity Systems of the Future: Incentives, Regulation and Analysis for Efficient Investment'', March 18 - 22, 2019, Isaac Newton Institute, Cambridge, UK, March 21, 2019.

  • M. Hintermüller, Lecture Series: Optimal control of nonsmooth structures, Thematic Programme ``Modern Maximal Monotone Operator Theory: From Nonsmooth Optimization to Differential Inclusions'',, February 4 - 7, 2019, Erwin Schrödinger International Institute for Mathematics and Physics, Vienna, Austria.

  • M. Hintermüller, Math4NFDI -- A consortium for mathematics, National Research Data Infrastructure Conference 2019, May 13 - 14, 2019, Bonn.

  • M. Hintermüller, Optimal control of multiphase fluids and droplets, Colloquium of the Mathematical Institute, University of Oxford, UK, June 7, 2019.

  • M. Hintermüller, Structural total variation regularization with applications in inverse problems, 90th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM), DFG Priority Programme 1962 ``Non Smooth and Complementarity-Based Distributed Parameter Systems: Simulation and Hierarchical Optimization'', February 18 - 22, 2019, Technische Universität Wien, Austria, February 19, 2019.

  • K. Papafitsoros, Generating structure non-smooth priors for image reconstruction, Young Researchers in Imaging Seminars, March 20 - 27, 2019, Henri Poincaré Institute, Paris, France, March 27, 2019.

  • C.N. Rautenberg, Parabolic quasi-variational inequalities with gradient and obstacle type constraints, Modern Maximal Monotone Operator Theory: From Nonsmooth Optimization to Differential Inclusions, January 28 - February 1, 2019, Erwin Schrödinger International Institute for Mathematics and Physics (ESI), Wien, Austria, January 31, 2019.

  • J.A. Brüggemann, Path-following methods for a class of elliptic obstacle-type quasi-variational problems with integral constraints, 23rd International Symposium on Mathematical Programming (ISMP2018), Session 370 ``Variational Analysis 4'', July 1 - 6, 2018, Bordeaux, France, July 2, 2018.

  • A. Alphonse, Optimal Control of Elliptic and Parabolic Quasi-Variational Inequalities, Annual Meeting of the DFG Priority Programme 1962, October 1 - 3, 2018, Kremmen (Sommerfeld), October 3, 2018.

  • A. Alphonse, Parabolic quasi-variational inequalities: Existence and sensitivity analysis, 4th Central European Set-Valued and Variational Analysis Meeting (CESVVAM 2018), November 24, 2018, Philipps-Universität Marburg, November 24, 2018.

  • A. Alphonse, Directional differentiability for elliptic QVIs of obstacle type, 89th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM 2018), Session PP07 ``DFG Priority Program 1962'', March 19 - 23, 2018, Technische Universität München, March 20, 2018.

  • A. Alphonse, Directional differentiability for elliptic QVIs of obstacle type, Joint Research Seminar on Mathematical Optimization / Non-smooth Variational Problems and Operator Equations, WIAS, May 23, 2018.

  • A. Alphonse, Directional differentiability for elliptic quasi-variational inequalities, Workshop ``Challenges in Optimal Control of Nonlinear PDE-Systems'', April 8 - 14, 2018, Mathematisches Forschungsinstitut Oberwolfach, April 12, 2018.

  • T. Keil, Simulation and Control of a Nonsmooth Cahn--Hilliard--Navier--Stokes System with Variable Fluid Densities, Annual Meeting of the DFG Priority Programme 1962, October 1 - 3, 2018, Kremmen (Sommerfeld), Germany, October 2, 2018.

  • T. Keil, Strong stationarity conditions for the optimal control of a Cahn--Hilliard--Navier--Stokes system, 5th European Conference on Computational Optimization, Session ``Infinite Dimensional Nonsmooth Optimization'', September 10 - 12, 2018, Trier, September 12, 2018.

  • S.-M. Stengl, Generalized Nash equilibrium problems with partial differential operators: theory, algorithms and risk aversion, Annual Meeting of the DFG Priority Programme 1962, October 1 - 3, 2018, Kremmen (Sommerfeld), October 1, 2018.

  • S.-M. Stengl, Uncertainty quantification of the Ambrosio--Tortorelli approximation in image segmentation, MIA 2018 -- Mathematics and Image Analysis, Humboldt-Universität zu Berlin, January 15 - 17, 2018.

  • C. Löbhard, Analysis, algorithms and applications for the optimal control of variational inequalities, European Women in Mathematics (EWM) General Meeting 2018, Minisymposium 9 ``Nonsmooth PDE-constrained Optimization: Problems and Methods'', September 3 - 7, 2018, Karl-Franzens-Universität Graz, Austria, September 7, 2018.

  • C. Löbhard, Optimal shape design of air ducts in combustion engines, ROMSOC Mid--Term Meeting, November 26 - 27, 2018, Universität Bremen, November 26, 2018.

  • M. Hintermüller, M. Holler, K. Papafitsoros, A function space framework for structural total variation regularization in inverse problems, MIA 2018 -- Mathematics and Image Analysis, Humboldt-Universität zu Berlin, January 15 - 17, 2018.

  • M. Hintermüller, Automated regularization parameter choice rule in image processing, Workshop ``New Directions in Stochastic Optimisation'', August 19 - 25, 2018, Mathematisches Forschungsinstitut Oberwolfach, August 23, 2018.

  • M. Hintermüller, Bilevel optimisation in automated regularisation parameter selection in image processing, WIAS--PGMO Workshop on Nonsmooth and Stochastic Optimization, June 26, 2018, Humboldt-Universität zu Berlin, June 26, 2018.

  • M. Hintermüller, Bilevel optimization and some "parameter learning" applications in image processing, SIAM Conference on Imaging Science, Minisymposium MS5 ``Learning and Adaptive Approaches in Image Processing'', June 5 - 8, 2018, Bologna, Italy, June 5, 2018.

  • M. Hintermüller, Generalised Nash equilibrium problems with partial differential equations, Search Based Model Engineering Workshop, August 7 - 9, 2018, King's College London, UK, August 7, 2018.

  • M. Hintermüller, Multiobjective optimization with PDE constraints, International Workshop on PDE-Constrained Optimization, Optimal Controls and Applications, December 10 - 14, 2018, Sanya, China, December 13, 2018.

  • M. Hintermüller, Multiobjective optimization with PDE constraints, 23rd International Symposium on Mathematical Programming (ISMP2018), July 1 - 6, 2018, Bordeaux, France, July 2, 2018.

  • M. Hintermüller, Nonsmooth structures in PDE constrained optimization, Mathematisches Kolloquium, Universität Bielefeld, Fakultät für Mathematik, June 7, 2018.

  • M. Hintermüller, Recent advances in non-smooth and complementarity-based distributed parameter systems, 89th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM 2018), Session PP07 ``DFG Priority Program 1962'', March 19 - 23, 2018, Technische Universität München, March 20, 2018.

  • M. Hintermüller, Semismooth Newton methods in PDE constrained optimization, Advanced Training in Mathematics Schools ``New Directions in PDE Constrained Optimisation'', March 12 - 16, 2018, National Centre for Mathematics of IIT Bombay and TIFR, Mumbai, Bombay, India.

  • M. Hintermüller, Structural total variation regularization with applications in inverse problems, International Conference on Scientific Computing, December 5 - 8, 2018, Department of Mathematics, The Chinese University of Hong Kong, China, December 8, 2018.

  • K. Papafitsoros, A function space framework for structural total variation regularization with applications in inverse problems, SIAM Conference on Imaging Science, Minisymposium MS38 ``Geometry-driven Anisotropic Approaches for Imaging Problems'', June 5 - 8, 2018, Bologna, Italy, June 6, 2018.

  • K. Papafitsoros, A function space framework for structural total variation regularization with applications in inverse problems, VI Latin American Workshop on Optimization and Control (LAWOC 18), September 3 - 7, 2018, Quito, Ecuador, September 4, 2018.

  • C.N. Rautenberg, Dissipative and non-dissipative evolutionary quasi-variational inequalities with derivative constraints, Joint Meeting of the Italian Mathematical Union, the Italian Society of Industrial and Applied Mathematics and the Polish Mathematical Society, Session 14 ``Nonlinear Variational Methods with Applications'', September 17 - 20, 2018, Wroclaw, Poland, September 19, 2018.

  • C.N. Rautenberg, On the optimal control of quasi-variational inequalities, 23rd International Symposium on Mathematical Programming (ISMP2018), Session 221 ``Optimization Methods for PDE Constrained Problems'', July 1 - 6, 2018, Bordeaux, France, July 3, 2018.

  • C.N. Rautenberg, Optimization problems with quasi-variational inequality constraints, Workshop ``Challenges in Optimal Control of Nonlinear PDE-Systems'', April 8 - 14, 2018, Mathematisches Forschungsinstitut Oberwolfach, April 11, 2018.

  • C.N. Rautenberg, Spatially distributed parameter selection in Total Variation (TV) models, MIA 2018 -- Mathematics and Image Analysis, Humboldt-Universität zu Berlin, January 15 - 17, 2018.

  • C.N. Rautenberg, Evolutionary quasi-variational inequalities: Applications, theory, and numerics, 5th International Conference on Applied Mathematics, Design and Control: Mathematical Methods and Modeling in Engineering and Life Sciences, November 7 - 9, 2018, San Martin National University, Buenos Aires, Argentina, November 9, 2018.