ELA, Volume 7, pp. 53-58, July 2000, abstract.

A class of inverse M-matrices

Reinhard Nabben

Nonnegative matrices whose inverses are M-matrices are 
called inverse M-matrices. It is still an open problem to  
characterize all inverse M-matrices.  
In this note a new class of inverse M-matrices is established. 
This class of nonsymmetric matrices generalizes the class of 
strictly ultrametric matrices.