CONTENTS 1. Introduction and preliminaries....................................................5 1.1. Introduction............................................................................5 1.2. Organization..........................................................................6 1.3. Prerequisites.........................................................................6 1.4. Introductory examples...........................................................9 2. Elementary properties.............................................................14 2.1. Basic facts...........................................................................14 2.2. Infimal convolution of subadditive functions.........................17 2.3. Semicontinuity, continuity, and exactness............................19 2.4. Two examples......................................................................22 3. The convex case.....................................................................23 3.1. Basic results........................................................................23 3.2. Differential calculus, and first order differentiability..............28 3.3. Formulas on f ▫ g.................................................................31 3.4. Loss of differentiability.........................................................32 4. Continuity of the operation of infimal convolution....................33 4.1. Introduction.........................................................................34 4.2. Epi-convergence.................................................................35 4.3. The Mosco topology and the slice topology.........................36 4.4. The affine topology..............................................................38 4.5. The Attouch-Wets topology.................................................39 5. Regularization.........................................................................41 5.1. Introduction and first results................................................41 5.2. Approximation in Hilbert spaces...........................................47 5.3. Generalized Moreau-Yosida approximation.........................52 References..................................................................................55
Department of Mathematics, University of Lund, P.O. Box 118, S-221 00 Lund, Sweden
Bibliografia
[1] W. N. Anderson and R. J. Duffin, Series and parallel addition of matrices, J. Math. Anal. Appl. 26 (1969), 576-594.
[2] H. Attouch, Variational Convergence for Functions and Operators, Appl. Math. Ser., Pitman, Boston, 1984.
[3] H. Attouch, Viscosity solutions of minimization problems. Epi-convergence and scaling, Sém. Anal. Convexe 22 (1992), 8.1-8.46.
[4] H. Attouch and D. Azé, Approximation and regularization of arbitrary functions in Hilbert spaces by the Lasry-Lions method, Sém. Anal. Convexe 20 (1990), 12.1-12.23; Ann. Inst. H. Poincaré Anal. Non Linéaire 10 (1993), 289-312.
[5] H. Attouch, D. Azé and G. Beer, On some inverse stability problems for the epigraphical sum, Nonlinear Anal. 16 (1991), 241-254.
[6] H. Attouch and G. Beer, On the convergence of subdifferentials of convex functions, Arch. Math. (Basel) 60 (1993), 389-400.
[7] H. Attouch and H. Brezis, Duality for the sum of convex functions in general Banach spaces, in: Aspects of Mathematics and its Applications, J. A. Barroso (ed.), North-Holland, Amsterdam, 1986, 125-133.
[8] H. Attouch and R. J.-B. Wets, Epigraphical analysis, in: Analyse Non Linéaire, H. Attouch, J.-P. Aubin, F. H. Clarke and I. Ekeland (eds.), Gauthier-Villars, Paris, et C.R.M., Montréal, 1989, 72-100.
[9] H. Attouch and R. J.-B. Wets, Quantitative stability of variational systems: I. The epigraphical distance, Trans. Amer. Math. Soc. 328 (1991), 695-729.
[10] J.-P. Aubin, L'analyse Non Linéaire et ses Motivations Économiques, Masson, Paris, 1984.
[11] G. Beer, On the Young-Fenchel transform for convex functions, Proc. Amer. Math. Soc. 104 (1988), 1115-1123.
[12] G. Beer, On Mosco convergence of convex sets, Bull. Austral. Math. Soc. 38 (1988), 239-253.
[13] G. Beer, Infima of convex functions, Trans. Amer. Math. Soc. 315 (1989), 849-859.
[14] G. Beer, The slice topology: a viable alternative to Mosco convergence in nonreflexive spaces, Nonlinear Anal. 19 (1992), 271-290.
[15] G. Beer, Lipschitz regularization and the convergence of convex functions, preprint.
[16] G. Beer, Topologies on Closed and Closed Convex Sets, Kluwer, Dordrecht, 1993.
[17] G. Beer and J. M. Borwein, Mosco convergence and reflexivity, Proc. Amer. Math. Soc. 109 (1990), 427-436.
[18] G. Beer and R. Lucchetti, The epi-distance topology: continuity and stability results with applications to convex optimization problems, Math. Oper. Res. 17 (1992), 715-726.
[19] J. Benoist, Convergence de la dérivée de la régularisée Lasry-Lions, C. R. Acad. Sci. Paris Sér. I Math. 315 (1992), 941-944.
[20] J. Bergh and J. Löfström, Interpolation Spaces, Springer, Berlin, 1976.
[21] J. Boman, The sum of two plane convex $C^∞$ sets is not always C⁵, Math. Scand. 66 (1990), 216-224.
[22] J. Boman, Smoothness of sums of convex sets with real analytic boundaries, Math. Scand. 66 (1990), 225-230.
[23] M. Bougeard, J.-P. Penot and A. Pommellet, Towards minimal assumptions for the infimal convolution regularization, J. Approx. Theory 64 (1991), 245-270.
[24] H. Brézis, Opérateurs Maximaux Monotones et Semi-Groupes de Contractions dans les Espaces de Hilbert, North-Holland, Amsterdam, 1973.
[25] C. Bylka and W. Orlicz, On some generalizations of the Young inequality, Bull. Acad. Polon. Sér. Sci. Math. Astronom. Phys. 26 (1978), 115-123.
[26] G. Choquet, Convergences, Ann. Univ. Grenoble 23 (1947-1948), 57-112.
[27] F. H. Clarke, Optimization and Nonsmooth Analysis, Wiley, New York, 1983.
[28] M. M. Day, Normed Linear Spaces, 3rd ed., Springer, 1973.
[29] R. Deville, G. Godefroy and V. Zizler, Smoothness and Renormings in Banach Spaces, Pitman Monographs Surveys Pure Appl. Math. 64, Longman Sci. Tech., 1993.
[30] A. L. Dontchev and T. Zolezzi, Well-Posed Optimization Problems, Lecture Notes in Math. 1543, Springer, Berlin, 1993.
[31] I. Ekeland, On the variational principle, J. Math. Anal. Appl. 47 (1974), 324-353.
[33] I. Ekeland and R. Temam, Convex Analysis and Variational Problems, North-Holland, Amsterdam, 1976.
[34] S.-L. Eriksson and H. Leutwiler, A potential-theoretic approach to parallel addition, Math. Ann. 274 (1986), 301-317.
[35] W. Fenchel, Convex Cones, Sets, and Functions, Lecture Notes, Princeton University, Princeton, 1953.
[36] S. Fitzpatrick and R. R. Phelps, Bounded approximants to monotone operators on Banach spaces, Ann. Inst. H. Poincaré Anal. Non Linéaire 9 (1992), 573-595.
[37] A. Fougeres et A. Truffert, Régularisation S.C.I. et Γ-convergence: approximations inf-convolutives associées à un référentie, Ann. Mat. Pura Appl. 152 (1988), 21-51.
[38] F. Hausdorff, Über halbstetige Funktionen und deren Verallgemeinerung, Math. Z. 5 (1919), 292-309.
[39] J.-B. Hiriart-Urruty, Extension of Lipschitz functions, J. Math. Anal. Appl. 77 (1980), 539-544.
[40] J.-B. Hiriart-Urruty, Lipschitz r-continuity of the approximative subdifferential of a convex function, Math. Scand. 47 (1980), 123-134.
[41] J.-B. Hiriart-Urruty, A general formula on the conjugate of the difference of functions, Canad. Math. Bull. 29 (1986), 482-485.
[42] J.-B. Hiriart-Urruty et M.-L. Mazure, Formulation variationnelle de l'addition parallèle et de la soustraction parallèle d'opérateurs semi-définis positifs, C. R. Acad. Sci. Paris 302 (1986), 527-530.
[43] J.-B. Hiriart-Urruty and R. R. Phelps, Subdifferential calculus using ε-subdifferentials, J. Funct. Anal. 118 (1993), 154-166.
[44] J.-B. Hiriart-Urruty and P. Plazanet, Moreau's decomposition theorem revisited, Ann. Inst. H. Poincaré Anal. Non Linéaire 6 (1989), 325-338.
[45] A. D. Ioffe and V. M. Tikhomirov, Theory of Extremal Problems, North-Holland, Amsterdam, 1979.
[46] V. Jeyakumar, Duality and infinite dimensional optimization, Nonlinear Anal. 15 (1990), 1111-1122.
[47] C. O. Kiselman, How smooth is the shadow of a smooth convex body?, J. London Math. Soc. 33 (1986), 101-109.
[48] C. O. Kiselman, Smoothness of vector sums of plane convex sets, Math. Scand. 60 (1987), 239-252.
[49] C. O. Kiselman, Regularity classes for operations in convexity theory, Kodai Math. J. 15 (1992), 354-374.
[50] F. Kubo, Conditional expectations and operations derived from network connections, J. Math. Anal. Appl. 80 (1981), 477-489.
[51] S. S. Kutateladze, Convex operators, Russian Math. Surveys 34 (1979), 181-214.
[52] J. Lahrache, Stabilité et convergence dans les espaces non réflexifs, Sém. Anal. Convexe Montpellier 21 (1991), 10.1-10.53.
[53] J.-M. Lasry and P.-L. Lions, A remark on regularization in Hilbert spaces, Israel J. Math. 55 (1986), 257-266.
[54] P.-J. Laurent, Approximation et Optimisation, Hermann, Paris, 1972.
[55] P. D. Lax, Hyperbolic systems of conservation laws, Comm. Pure Appl. Math. 10 (1957), 537-566.
[63] J.-J. Moreau, Inf-convolution des fonctions numériques sur un espace vectoriel, C. R. Acad. Sci. Paris 256 (1963), 5047-5049.
[64] J.-J. Moreau, Proximité et dualité dans un espace Hilbertien, Bull. Soc. Math. France 93 (1965), 273-299.
[65] J.-J. Moreau, Fonctionnelles Convexes, Lecture notes, Collège de France, Paris, 1967.
[66] J.-J. Moreau, Inf-convolution, sous-additivité, convexité des fonctions numériques, J. Math. Pures Appl. 49 (1970), 109-154.
[67] J.-J. Moreau, Weak and strong solutions of dual problems, in: Contributions to Nonlinear Functional Analysis, E. Zarantello (ed.), Academic Press, 1971, 181-214.
[68] T. D. Morley, Parallel summation, Maxwell's principle and the infimum of projections, J. Math. Anal. Appl. 70 (1979), 33-41.
[69] U. Mosco, Convergence of convex sets and of solutions of variational inequalities, Adv. in Math. 3 (1969), 510-585.
[70] U. Mosco, On the continuity of the Young-Fenchel transform, J. Math. Anal. Appl. 35 (1971), 518-535.
[71] G. B. Passty, The parallel sum of nonlinear monotone operators, Nonlinear Anal. 10 (1986), 215-227.
[72] J.-P. Penot and M. L. Bougeard, Approximation and decomposition properties of some classes of locally d.c. functions, Math. Programming 41 (1988), 195-227.
[73] R. R. Phelps, Convex Functions, Monotone Operators and Differentiability, Lecture Notes in Math. 1364, Springer, 1989.
[74] R. Poliquin, J. Vanderwerff and V. Zizler, Convex composite representation of lower semicontinuous functions and renorming, C. R. Acad. Sci. Paris 317 (1993), 545-549.
[75] R. T. Rockafellar, Extension of Fenchel's duality theorem, Duke Math. J. 33 (1966), 81-89.
[76] R. T. Rockafellar, Convex Analysis, Princeton University Press, Princeton, 1970.
[77] B. Rodrigues, The Fenchel duality theorem in Fréchet spaces, Optimization 21 (1990), 13-22.
[78] B. Rodrigues and S. Simons, Conjugate functions and subdifferentials in nonnormed situations for operators with complete graphs, Nonlinear Anal. 12 (1988), 1069-1078.
[79] W. Rudin, Functional Analysis, MacGraw-Hill, New York, 1973.
[80] A. Seeger, Direct and inverse addition in convex analysis and applications, J. Math. Anal. Appl. 148 (1990), 317-343.
[81] S. Simons, The occasional distributivity of ∘ over $+_e$ and the change of variable formula for conjugate functions, Nonlinear Anal. 14 (1990), 1111-1120.
[82] T. Strömberg, An operation connected to a Young-type inequality, Math. Nachr. 159 (1992), 227-243.
[83] T. Strömberg, Representation formulae for infimal convolution with applications, in: Analysis, Algebra, and Computers in Mathematical Research, M. Gyllenberg and L. E. Persson (eds.), Lecture Notes in Pure and Appl. Math. 156, Dekker, New York, 1994, 319-334.
[84] J. Vanderwerff, Smooth approximations in Banach spaces, Proc. Amer. Math. Soc. 115 (1992), 113-120.
[85] M. Volle, Sur quelques formules de dualité convexe et non convexe, Set-Valued Analysis, to appear.
[86] M. Volle, Compléments sur la relation entre la régularisation de Lasry-Lions et l'équation de Hamilton-Jacobi, Sém. Anal. Convexe 20 (1990), 7.1-7.10.
[87] M. Volle, Régularisation des fonctions fortement minorées dans les espaces de Hilbert, Sém. Anal. Convexe 20 (1990), 8.1-8.8.
[88] M. Volle, Some applications of the Attouch-Brezis condition to closedness criterions, optimization, and duality, Sém. Anal. Convexe 22 (1992), 16.1-16.15.
[89] M. Volle, A formula on the subdifferential of the deconvolution of convex functions, Bull. Austral. Math. Soc. 47 (1993), 333-340.
[90] R. J.-B. Wets, Convergence of convex functions, variational inequalities and convex optimization problems, in: Variational Inequalities and Complementary Problems, P. Cottle et al. (eds.), Wiley, Chichester, 1980, 375-403.
[91] C. Zălinescu, On uniformly convex functions, J. Math. Anal. Appl. 95 (1983), 344-374.
[92] C. Zălinescu, On some open problems in convex analysis, Arch. Math. (Basel) 59 (1992), 566-571.