Some results on the group inverse for block matrices over skew fields.
We establish a unique factorization result into irreducibel elements in the partial semigroup of 2 × 2-matrices with entries in K[x] whose determinant is equal to 1, where K is a field, and where multiplication is defined as the usual matrix-multiplication if the degrees of the factors add up. This investigation is motivated by a result on matrices of entire functions.
By a sign pattern (matrix) we mean an array whose entries are from the set . The sign patterns for which every real matrix with sign pattern has the property that its inverse has sign pattern are characterized. Sign patterns for which some real matrix with sign pattern has that property are investigated. Some fundamental results as well as constructions concerning such sign pattern matrices are provided. The relation between these sign patterns and the sign patterns of orthogonal matrices...