“…In such a case we shall also call the pairs (i,,j,) and (i,+ 1,J,+l) disjoint. This fact has been widely used in defining special orderings that make Jacobi methods amenable for parallel processing, and also for proving the global convergence of such processes (see [17,16] etc.). Here we shall use similar ideas for proving sharp quadratic convergence bounds of the serial processes.…”