Solvability of semidefinite complementarity problems

The concept of exceptional family has been introduced to study the existence theorem for nonlinear complementarity problems and variational inequality problems. We describe extensions of such concepts to complementarity problems defined over the cone of block-diagonal symmetric positive semidefinite real matrices. Using the concept of exceptional family, we propose a very general existence theorem for the semidefinite complementarity problem. Extensions of Isac-Carbone's condition, Karamardian's condition, properness and coercivity are also introduced. Several applications of the main results are presented, and we prove that without exceptional family is a sufficient and necessary condition for the solvability of pseudomonotone semidefinite complementarity problems.