Exact expressions for the Drazin inverse of anti-triangular matrices

The main contribution of this paper is to develop explicit expressions for the Drazin inverse of two kinds of anti-triangular block complex matrices under new assumptions. Further, we apply our results to obtain new formulae for the Drazin inverse of a 2 × 2 block complex matrix. We present a list of well-known results which are recovered in this paper. We give three examples to illustrate our new explicit expressions.