A new class of functions, termed semistrictly preinvex functions, is introd
uced in this paper. Same properties of semistrictly preinvex functions are
discussed. In particular, the relationship between semistrictly preinvex fu
nctions and preinvex functions is investigated. Some characterization prope
rties of semistrictly preinvex functions are derived under a lower semicont
inuous condition, and a gradient property of semistrictly preinvex function
s is obtained. (C) 2001 Academic Press.