The Drazin inverse of a square matrix. For an invertible matrix it is the
DrazinInverse[m]
DrazinInverse[{{1, 2}, {3, 4}}]
→ {{-2, 1}, {3/2, -1/2}}DrazinInverse[{{2, 1}, {0, 0}}]
→ {{1/2, 1/4}, {0, 0}}DrazinInverse[{{0, 1}, {0, 0}}]
→ {{0, 0}, {0, 0}}