Full paper in PDF format:
$%A. Favini, R. Labbas, K. Lemrabet, and B.-K. Sadallah, Study of a complete abstract differential equation of elliptic type with variable operator coefficients, I, Rev. Mat. Complut. 21 (2008), no. 1, 89–133.%$

Study of a Complete Abstract
Differential Equation of Elliptic Type
with Variable Operator Coefficients, I
Angelo FAVINI, Rabah LABBAS,
Keddour LEMRABET, and Boubaker-Khaled SADALLAH
Università degli Studi di Bologna
Dipartimento di Matematica
Piazza di Porta S.
Donato 5, 40126 Bologna — Italy

favini@dm.unibo.it
Laboratoire de Mathématiques Appliquées
Université du Havre
U.F.R Sciences et Techniques, B.P 540
76058 Le Havre — France

rabah.labbas@univ-lehavre.fr
Laboraoire AMNEDP
Faculté des Maths, USTHB
BP 32, El Alia, Bab Ezzouar
16111 Alger — Algeria

keddourlemrabet@yahoo.fr
Laboratoire EDP et Hist. Maths
Ecole Normale Supérieure
16050 Kouba, Alger — Algeria

sadallah@ens-kouba.dz
Received: May 16, 2007
Accepted: August 30, 2007

ABSTRACT

The aim of this first work is the resolution of an abstract complete second order differential equation of elliptic type with variable operator coefficients set in a small length interval. We obtain existence, uniqueness and maximal regularity results under some appropriate differentiability assumptions combining those of "On the abstract evolution equation of parabolic type" (Yagi, 1977) and "Sommes d'opérateurs linéaires et équations différentielles opérationnelles" (Da Prato-Grisvard, 1975). An example for the Laplacian in a regular domain of ℝ3  will illustrate the theory. A forthcoming work (Part II) will complete the present one by the study of the Steklov-Poincaré operator related to this equation when the length δ  of the interval tends to zero.

Key words: abstract differential equations of second order, variable operator coefficients, mixed boundary conditions, maximal regularity, compatibility conditions.
2000 Mathematics Subject Classification:
34G10, 34K10,34K30, 35J25, 44A45, 47D03.