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