I want to solve Ax = b, using some iterative solvers. I don’t have matrix `A`

available at hand (too expensive to compute), but I can readily calculate `A * x`

for any given `x`

.

I tried looking at options that are exposed in this awesome package, LinearSolve.jl and in this package IterativeSolvers.jl, but didn’t find any such option.

I would like to use GMRES or Algebraic Multigrid for solving this system.

MATLAB has an option in GMRES in to compute Ax using a function handle instead of using a numeric A matrix, so I’m hoping I’ve overlooked something that’s available in julia.

I can solve this using NLsolve by calculating the residue `Ax-b`

and minimizing it, but something simpler using an iterative solver would be better.

Thanks in advance.