Z. DOSTÁL: Polynomials of the eigenvalues and powers of matrices
. Comment. Math. Univ. Carolinae (in print) MR 0508954
 V. PTÁK: Spectral radius, norms of iterates and the critical exponent
. Linear Algebra and its Applications 1 (1968), 245-260. MR 0230744
 V. PTÁK: A maximum problem for matrices. (submitted to the journal Linear Algebra and its Applications).