H. Bart et Apm. Wagelmans, An integer programming problem and rank decomposition of block upper triangular matrices, LIN ALG APP, 305(1-3), 2000, pp. 107-129
A necessary and sufficient condition is given for a block upper triangular
matrix A to be the sum of block upper rectangular matrices satisfying certa
in rank constraints. The condition is formulated in terms of the ranks of c
ertain submatrices of A. The proof goes by reduction to an integer programm
ing problem. This integer programming problem has a totally unimodular cons
traint matrix which makes it possible to utilize Farkas' Lemma. (C) 2000 El
sevier Science Inc. All rights reserved.