关于偶模的维数

On Dimensions of Dual Modules

设SUR为双模,给出了投射模的U-偶模为平坦模,投射模等特殊模的若干刻画,并利用U-偶模得到了关于Ex tnR(M,U)的正合列,从而证明了在右凝聚环、凝聚左完全环下,Ex tmR(M,U)(m≥0)的平坦维数、投射维数、有限表现维数等均不超过M的相应维数.

Let sUn be a bimodule, give some characterizations that each U-dual of projective modulesis flat, projective respectively. Using U-dual modules obtain an exact sequence of Ext^nR（M,U） , and show that for a right coherent ring R , or a coherent left perfect ring R, the flat dimensions, projective dimensions and finitely presented dimensions of Ext^mR（M,U） （m≥0） are less than the corresponding dimensions of M.