Journal of the
Korean Mathematical Society JKMS

Sign patterns of idempotent matrices, especially symmetric idempotent matrices, are investigated. A number of fundamental results are given and various constructions are presented. The sign patterns of symmetric idempotent matrices through order 5 are determined. Some open questions are also given.

Keywords: sign pattern matrix, require, allow, generalized sign pattern matrix, idempotent matrix, symmetric idempotent matrix, symmetric orthogonal matrix

MSC numbers: 15A21, 15A24, 15A57