I am thinking about the common case where you’re asking for the method for doing the lienar solving which will be repeated open during some calculation. For example, what linear solver to use when solving a numerical ODE with a Rosenbrock method. That would need a function since it would need to know how to solve the linear system resulting from the Jacobian each iteration, so you cannot just pass a matrix.
Is there any way to do this with IterativeSolvers.jl? I.e. pass a function such that linear_solve(A) will then be \ and apply say GMRES?