“…One alternative is to solve them directly by exploiting the matrix structure (see for example [6,16,47,73]). A more popular approach is to employ some iterative method to solve the system, assisted by an appropriately designed preconditioner, to ensure that the iterative method achieves fast convergence (as in [8,9,10,11,12,13,14,15,42,44,45,46,56,71]). An equally rich literature exists for preconditioning Toeplitz-like linear systems arising specifically from the discretization of fractional diffusion equations (see [17,24,25,29,32,45,46,48,53], among others).…”