Mutual incidence matrix of two balanced incomplete block designs

Abstract

We propose to consider a mutual incidence matrix $M$ of two balanced incomplete block designs built on the same finite set. In the simplest case, this matrix reduces to the standard incidence matrix of one block design. We find all eigenvalues of the matrices $M{M}^T$ and $M^{T}M$ and their eigenspaces.

arXiv comment13 pages