Hysteresis is an exciting and mathematically challenging phenomenon that
oc- curs in rather different situations: jt, can be a byproduct
offundamental physical mechanisms (such as phase transitions) or the
consequence of a degradation or imperfection (like the play in a
mechanical system), or it is built deliberately into a system in order
to monitor its behaviour, as in the case of the heat control via
thermostats. The delicate interplay between memory effects and the
occurrence of hys- teresis loops has the effect that hysteresis is a
genuinely nonlinear phenomenon which is usually non-smooth and thus not
easy to treat mathematically. Hence it was only in the early seventies
that the group of Russian scientists around M. A. Krasnoselskii
initiated a systematic mathematical investigation of the phenomenon of
hysteresis which culminated in the fundamental monograph
Krasnoselskii-Pokrovskii (1983). In the meantime, many mathematicians
have contributed to the mathematical theory, and the important
monographs of 1. Mayergoyz (1991) and A. Visintin (1994a) have appeared.
We came into contact with the notion of hysteresis around the year 1980.