A polynomial recognition algorithm for balanced matrices

A 0 , ± 1 matrix is balanced if it does not contain a square submatrix with two nonzero elements per row and column in which the sum of all entries is 2 modulo 4. Conforti et al. (J. Combin. Theory B 77 (1999) 292; B 81 (2001) 275), provided a polynomial algorithm to test balancedness of a matrix. In this paper we present a simpler polynomial algorithm, based on techniques introduced by Chudnovsky and Seymour (Combinatorica, to appear) for Berge graphs.