ELA, Volume 10, pp. 102-105, May 2003, abstract.

Recognition of Hidden Positive Row Diagonally Dominant Matrices

Walter D. Morris, Jr.

A hidden positive row diagonally dominant (hprdd) matrix is a
square matrix A for which there exist square matrices C and B 
so that AC = B and each diagonal entry of B and C is greater 
than the sum of the absolute values of the off-diagonal entries 
in its row. A linear program with 5n^2 - 4n variables and 2n^2 
constraints is defined that takes as input an n-by-n matrix A 
and produces C and B satisfying the above conditions if and only 
if they exist. A 4-by-4 symmetric positive definite matrix that 
is not an hprdd matrix is presented.