# Elliptic Partial Differential Equations

## Periodo di svolgimento

da Venerdì, 8 Novembre 2019 a Venerdì, 22 Maggio 2020
Ore del corso: 40
Ore dei docenti responsabili: 40

## Modalità d'esame

• Relazione o seminario
• Prova orale

## Prerequisiti

Nozioni di base di teoria della misura, spazi di Sobolev e Analisi Funzionale.

Laurea specialistica e Perfezionamento

Master or PhD

Basic notions of measure theory, Sobolev spaces and Functional Analysis

## Programma

1 Some basic facts regarding Sobolev spaces

2 Variational formulation of some PDEs

2.1 Elliptic operators

2.2 Inhomogeneous boundary conditions

2.3 Elliptic systems

2.4 Other variational aspects

3 Lower semicontinuity of integral functionals

4 Regularity Theory

4.1 Nirenberg method

5 Decay estimates for systems with constant coefficients

6 Regularity up to the boundary

7 Interior regularity for nonlinear problems

8 H¨older, Morrey and Campanato spaces

9 XIX Hilbert problem and its solution in the two-dimensional case

10 Schauder theory

11 Regularity in L^p spaces

12 Some classical interpolation theorems

13 Lebesgue differentiation theorem

14 Calderòn-Zygmund decomposition

15 The BMO space

16 Stampacchia Interpolation Theorem

17 De Giorgi’s solution of Hilbert’s XIX problem

17.1 The basic estimates

17.2 Some useful tools

17.3 Proof of H¨older continuity

18 Regularity for systems

18.1 De Giorgi’s counterexample to regularity for systems

19 Partial regularity for systems 93

19.1 The first partial regularity result for systems.

19.2 Hausdorff measures

19.3 The second partial regularity result for systems.

20 Some tools from convex and non-smooth analysis

20.1 Subdifferential of a convex function .

20.2 Convex functions and Measure Theory.

21 Viscosity solutions.

21.1 Basic definitions.

21.2 Viscosity solution versus classical solutions.

21.3 The distance function.

21.4 Maximum principle for semiconvex functions.

21.5 Existence and uniqueness results.

21.6 H¨older regularity.

22 Regularity theory for viscosity solutions.

22.1 The Alexandrov-Bakelman-Pucci estimate.

22.2 The Harnack Inequality.

Obiettivi formativi: In the course the basic techniques of the theory of elliptic partial differential equations are presented. Starting from the very classical methods based on energy inequalities and difference quotients, more recent tools, results and concepts are introduced, touching also the theory of viscosity solutions.

## Riferimenti bibliografici

L.C.EVANS. Partial Differential Equations, American Mathematical Society, 1998.

M.GIAQUINTA, L.MARTINAZZI. An introduction to the regularity theory for elliptic systems, harmonic maps and minimal graphs. Edizioni della Normale, 2005.

L.AMBROSIO,  A.CARLOTTO, A.MASSACCESI, Lectures on Elliptic Partial Differential Equations, pu blished by Edizioni SNS in 2019.