Like many leading figures in the world of management theory, Bruce Doolin Henderson, the founder of the Boston Consulting Group (and the man most responsible for the Boston matrix), was an engineer.

In a raging discussion on the Agile Testing Group, Jorge Argus initiated an interesting thread on the need for a traceability matrix in an Agile project.

The definition of similar quasi-direct sum of matrix is introduced. Andthe connection with group inverse is discussed. Some properties and applications are obtained.