“…There are several methods to solve Problems 2.1. In this article, we will make use of three methods: Landweber's (see, e.g., [15,Chapter 6]), Nesterov's (see [47,46]), and the conjugate gradient (CG) methods (see [29,27,13,34,26,20,48,16,4,22,42]). As we will see, the knowledge of the adjoint operator is essential for all of these iterative methods.…”