A class of two-step Steffensen type methods with fourth-order convergence

Based on Steffensen's method, we derive a one-parameter class of fourth-order methods for solving nonlinear equations. In the proposed methods, an interpolating polynomial is used to get a better approximation to the derivative of the given function. Each member of the class requires three evaluations of the given function per iteration. Therefore, this class of methods has efficiency index which equals 1.587. Kung and Traub conjectured an iteration using n evaluations of f or its derivatives without memory is of convergence order at most 2n-1. The new class of fourth-order methods agrees with the conjecture of Kung-Traub for the case n=3. Numerical comparisons are made to show the performance of the presented methods.