1. Center for Research in Scientific Computation, Box 8205, CRSC, NC State University, Raleigh, NC 27695-8205, USA
2. Laboratoire d'Analyse Numérique, Université Pierre et Marie Curie, Tour 55-65, 5éme étage, 4 place Jussieu, 75252 Paris Cedex 05, France
3. 215 Carnegie Hall, Department of Mathematics, Syracuse University, Syracuse, NY 13224-1150, USA