© 2004 by Oxford University Press
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On the approximation numbers of Sobolev embeddings on singular domains and trees
21 School of Mathematics, Cardiff University, 23 Senghennydd Road, Cardiff CF24 4YH 2 Department of Mathematics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
Upper and lower bounds are determined for a function which counts the approximation numbers of the Sobolev embedding W1,p (
)/C
Lp (
)/C, for a wide class of domains
of finite volume in Rn and 1 < p <
. Results on the distribution of the eigenvalues of the Neumann Laplacian in L2(
) are special consequences.
Received 27 May 2003. Revised 12 November 2003.