Suppose that an evaluated DMU may be not one of n DMU S and their inputs or outputs may be negative. In such a case this paper presents the necessary conditions or sufficient conditions on the existence of optimal solution for mixed model in DEA.

• 设被评价的决策单元可以不是这n个之一，且它们的输入或输出可以取负值，在这样情况下，给出了混合的DEA模型存在最优解的必要条件或充分条件