For functions that are separately solutions of an elliptic homogeneous PDE with constant coefficients, we prove an analogue of Siciak's theorem for separately holomorphic functions.
Over a non-archimedean local field the absolute value, raised to any positive power , is a negative definite function and generates (the analogue of) the symmetric stable process. For , this process is transient with potential operator given by M. Riesz’ kernel. We develop this potential theory purely analytically and in an explicit manner, obtaining special features afforded by the non-archimedean setting ; e.g. Harnack’s inequality becomes an equality.
We study the approximation of harmonic functions by means of harmonic polynomials in two-dimensional, bounded, star-shaped domains. Assuming that the functions possess analytic extensions to a δ-neighbourhood of the domain, we prove exponential convergence of the approximation error with respect to the degree of the approximating harmonic polynomial. All the constants appearing in the bounds are explicit and depend only on the shape-regularity of the domain and on δ. We apply the obtained estimates...
Dans le cadre de l’axiomatique de M. Brelot, et en utilisant la théorie des fonctions harmoniques adjointes de Madame R.M. Hervé, on caractérise la propriété de quasi-analycité notée : toute fonction harmonique adjointe dans un domaine est nulle dès qu’elle est nulle au voisinage d’un point. On montre que est équivalente à une propriété d’approximation de toute fonction réelle finie continue sur les frontières d’ouverts relativement compacts. Cette approximation est réalisée à l’aide de différences...
Let be harmonic in a bounded domain with smooth boundary. We prove that if the boundary values of belong to , where and denotes the surface measure of , then it is possible to approximate uniformly by function of bounded variation. An example is given that shows that this result does not extend to .