invex

Etymology
Introduced by Morgan A. Hanson in 1981 as a generalization of convex.

Adjective

 * 1)  A differentiable function &fnof; from Rn to R is invex if there exists a vector valued function g such that $$f(x) - f(u) \geq g(x, u) \cdot \nabla f(u), \, $$ for all x and u.