Abstract:
For a given homogeneous elliptic partial differential operator L with constant complex coefficients, the Banach space V of distributions in RN and a compact set X in RN, we study the quantity λV,L(X) equal to the distance in V from the class of functions f0 satisfying the equation Lf0=1 in a neighborhood of X (depending on f0) to the solution space of the equation Lf=0 in the neighborhoods of X. For V=BCm, we obtain upper and lower bounds for λV,L(X) in terms of the metric properties of the set X, which allows us to obtain estimates for λV,L(X) for a wide class of spaces V.