BondarenkoL.N. and ZhukP.F. 1997. Exact estima tes for the rate of convergence of the <em class="a-plus-plus">s</em&gt;-step method of steepest descent in eigenvalue problems. Ukrains’kyi Matematychnyi Zhurnal. 49, 12 (Dec. 1997), 1694–1699.