Ioan Rasa has published papers on Ulam's type stability of differential operators and several types of positive linear operators arising in approximation theory. He is author/co-author of many papers connecting Ulam's stability with other areas of mathematics (functional analysis, approximation theory, differential equations). Rasa is co-author (with. F. Altomare et al.) of the book Markov Operators, Positive Semigroups and Approximation Processes, de Gruyter, 2014.
