Author Description

These lecture notes are based on several courses and lectures given at di?erent places (University Pierre et Marie Curie, University of Bordeaux, CNRS research groups GRIP and CHANT, University of Roma I) for an audience of mathema- cians.ThemainmotivationisindeedthemathematicalstudyofPartialDi?erential Equationsthatarisefrombiologicalstudies.Among them, parabolicequations are the most popular and also the most numerous (one of the reasonsis that the small size,atthecelllevel,isfavorabletolargeviscosities).Manypapersandbookstreat this subject, from modeling or analysis points of view. This oriented the choice of subjects for these notes towards less classical models based on integral eq- tions (where PDEs arise in the asymptotic analysis), transport PDEs (therefore of hyperbolic type), kinetic equations and their parabolic limits. The?rstgoalofthesenotesistomention(anddescribeveryroughly)various?elds of biology where PDEs are used; the book therefore contains many ex- ples without mathematical analysis. In some other cases complete mathematical proofs are detailed, but the choice has been a compromise between technicality and ease of interpretation of the mathematical result. It is usual in the?eld to see mathematics as a blackboxwhere to enter speci?c models, often at the expense of simpli?cations. Here, the idea is di?erent; the mathematical proof should be close to the ‘natural’ structure of the model and re?ect somehow its meaning in terms of applications. Dealingwith?rstorderPDEs,onecouldthinkthatthesenotesarerelyingon the burden of using the method of characteristics and of de?ning weak solutions. We rather consider that, after the numerous advances during the 1980s, it is now clearthat‘solutionsinthesenseofdistributions’(becausetheyareuniqueinaclass exceeding the framework of the Cauchy-Lipschitz theory) is the correct concept.