On eigenvalues of real symmetric interval matrices: Sharp bounds and disjointness

In this paper, the eigenvalue problem of real symmetric interval matrices is studied. First, in case $2 \times 2$ matrices, all four endpoints two intervals are determined. These not necessarily eigenvalues vertex but it shown that such a matrix can be constructed from original one. Then, necessary and sufficient conditions provided for disjointness intervals. general $n\times n$ case, due to Hertz, set special determines maximal similar statement holds minimal namely if right off-diagonal smaller than absolute value left ones, he concluded provides eigenvalue. Generalizing it, with sign pattern, single one extremal bounds.