只要证明|M1+M2|/|M1|+|M1+M2|/|M2| ≥ 8.而|M1+M2|/|M1| = |E+M1^(-1)M2|,|M1+M2|/|M2| = |E+M2^(-1)M1|.设A = M1^(-1)M2,只要证明|E+A|+|E+A^(-1)| ≥ 8.由M1正定,存在可逆实矩阵P使M1 = PP' (P'为P的转置).于是A ...