We study a family of high-order Ehrlich-type methods for approximating all zeros of a polynomial simultaneously. Let us denote by T(1) the famous Ehrlich method (1967). Starting from T(1) , Kjurkchiev and Andreev (1987) have introduced recursively a sequence (T (N) ) ∞ N=1 of iterative methods for simultaneous finding polynomial zeros. For given N ≥ 1, the Ehrlich-type method T (N) has the order of convergence 2N + 1. In this paper, we establish two new local convergence theorems as well as a semilocal convergence theorem (under computationally verifiable initial conditions and with an a posteriori error estimate) for the Ehrlich-type methods T (N) . Our first local convergence theorem generalizes a result of Proinov (2015) and improves the result of Kjurkchiev and Andreev (1987). The second local convergence theorem generalizes another recent result of , but only in the case of the maximum norm. Our semilocal convergence theorem is the first result in this direction.
MSC: Primary 65H04; secondary 12Y05