Visiting Professor, University of Kyoto, March 2004

Gordon McKay Visiting Professor, University of California at Berkeley, October, 2002

Visiting Professor, Technion, Haifa, March - June, 1994

Distinguished Visiting Professor, Arizona State University, March, 1989

Visiting Scientist, International Institute of Applied Systems Analysis, Vienna, Austria, July - August, 1989

Visiting Professor, Chinese Academy of Sciences, Shanghai,  China, July - August ,1988

Visiting Scientist, Soviet Academy of Sciences, Moscow, USSR, October - November, 1985

Visiting Professor, University of Padova and Consiglio Nazionale delle Ricerche, Italy, on repeated occasions during 1975-1992

SIAM Visiting Lecturer, 1975--1976

Visiting Lecturer, State University of New York at Albany, summer 1973