设R是整环,Mn(R)是R上的n阶矩阵环。文中借助于矩阵计算方法,证明了轶为n的投射R-模P的自同态环可以表示为S=Y TMm(R)X,其中(X,Y)为P的一个m-基耦,还证明了P是自由R-模当且仅当R n*P作为Mn(R)-模是循环模,当且仅当R n*P≠ ∪(Rn*P)Mi,其中Mi取遍S的极大左理想。
R be a domain and M, (R) be the ring of n × n matrices over R. By matrix technique, it is shown that the ring of endomorphisms of a projective module P of rank n can he expressed as S = Y TMm(R) X, where (X,Y) is a m -projective basis couple. It is also proved that P is free if and only if Rn * Pas an M,(R) - module is cyclic; if and only if R n*P≠ ∪(Rn*P)Mi Rn, where Mi ranges over all maximal left ideals of S.