In this paper, we present a method how to get the expression for the group inverse of 2×2 block matrix and get the explicit expressions of the block matrix (A C B D) under some conditions.
设R为环,R的右理想I称为小理想如果对任意R的真右理想K都有I+K≠R.环R称为右小内射环如果每个从R的小右理想I到R R的同态可扩张为从R R到R R的同态.左小内射环定义类似.讨论了环的扩张如平凡扩张、形式三角矩阵环、上三角矩阵环等的小内射性.证明了环R通过双模R V R的平凡扩张S=R∝V为右自内射环当且仅当S为右小内射环当且仅当V作为右R-模为自内射模且R=End V R.并证明了非平凡的上三角矩阵环一定不是右小内射环.
Let a, b be two generalized Drazin invertibleelements in a Banach algebra. An explicit expression for thegeneralized Drazin inverse of the sum a ＋ b in terms of a, b,as, bd is given. The generalized Drazin inverse for the sum oftwo elements in a Banach algebra is studied by means of thesystem of idempotents. It is first proved that a ＋ b ∈ Aqnll underthe condition that a, b ∈ Aqnil, aba = 0 and ab^2 = 0 and then theexplicit expressions for the generalized Drazin inverse of thesum a ＋ b under some new conditions are given. Also, someknown results are extended.
假设R是一个有单位元1的结合环.探讨了R上分块矩阵Moore-Penrose逆的存在性,得到了环上分块矩阵的Moore-Penrose逆存在性的充要条件.进而,在EBF=0条件下,其中E=I-CC^+和F=I-A^+A,给出了Moore-Penrose逆的表达式M=[0 A C B].此结果推广了Pedro Patricio关于友矩阵M=[0 a I_n b]的Moore-Penrose逆表达式.作为应用,给出一些例子验证了所得到的结果.
