Approximation theorems for certain positive linear operators

In this work we prove approximation theorems for certain positive linear operators via Ditzian–Totik moduli ω 2 , ϕ ( f , ⋅ ) of second order where the step-weights are functions whose squares are concave. The results obtained are applied to the q -Lupaş–Bernstein operators, the ω , q -Bernstein operators and the convergence of the iterates of the q -Bernstein polynomials.