Bücher von Roberto Lucchetti

This volume contains several surveys focused on the ideas of approximate solutions, well-posedness and stability of problems in scalar and vector optimization, game theory and calculus of variations. These concepts are of particular interest in many fields of mathematics. The idea of stability goes back at least to J. Hadamard who introduced it in the setting of differential equations; the concept of well-posedness for minimum problems is more recent (the mid-sixties) and originates with A.N. Tykhonov. It turns out that there are connections between the two properties in the sense that a well-posed problem which, at least in principle, is "e;easy to solve"e;, has a solution set that does not vary too much under perturbation of the data of the problem, i.e. it is "e;stable"e;. These themes have been studied in depth for minimum problems and now we have a general picture of the related phenomena in this case. But, of course, the same concepts can be studied in other more complicated situations as, e.g. vector optimization, game theory and variational inequalities. Let us mention that in several of these new areas there is not even a unique idea of what should be called approximate solution, and the latter is at the basis of the definition of well- posed problem.

La varieta e l'interesse dei contributi alla Lettera Matematica Pristem hanno spinto i curatori, d'accordo con il comitato di redazione, a proporre in questa raccolta alcuni articoli apparsi sulla rivista dalla sua fondazione ad oggi. atica Pristem e una rivista, edita dalla Springer-Verlag Italia, che affronta temi legati alla ricerca matematica, ai fondamenti di questa disciplina, alla sua storia e alle sue applicazioni negli ambiti piu vari. La sfida e quella di interessare e divertire il lettore, riuscendo allo stesso tempo a convincerlo che la matematica, di solito ritenuta affare di pochi iniziati, lontana dagli interessi della gente comune, arido esercizio di astrusi calcoli, e invece fondamentale nella nostra vita quotidiana, ed e davvero dappertutto attorno a noi: nelle carte di credito, nella posta elettronica, in internet, nell'arte, nei giochi, nelle scelte (anche di tipo etico) che facciamo in situazioni conflittuali, e perfino in politica.

We shall consider convex functions from the most modern point of view: a function is de?ned to be convex whenever its epigraph, the set of the points lying above the graph, is a convex set. Except for trivial cases, the minimum value must be taken at a point where the function is not +?, hence at a point in the constraint set.