Academic Editor: C. Conca
    
        Copyright © 2012 Linlin Zhao. This is an open access article distributed under the   Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
        
     
Abstract
By using the matrix decomposition and the reverse order law, we provide some new expressions of the Drazin inverse for any  block matrix with rank constraints.