  The sign patterns of inverse doubly-nonnegative matrices are examined. A
necessary and sufficient condition is developed for a sign matrix to correspond
to an inverse doubly-nonnegative matrix. In addition, for a doubly-nonnegative
matrix whose graph is a tree, the inverse is shown to have a unique sign
pattern, which can be expressed in terms of a two-coloring of the graph.

Systems and Control;Numerical Analysis;Signal Processing;Numerical Analysis;Optimization and Control