def gmres_params(n_krylov=40, max_restarts=20, tol_coef=0.01):
    """
    Bundles parameters for the GMRES linear solver. These control the
    expense of finding the left and right environment Hamiltonians.

    PARAMETERS
    ----------
    n_krylov (int): Size of the Krylov subspace.
    max_restarts (int): Maximum number of times to iterate the Krylov
                        space construction.
    tol_coef (float): This number times the MPS gradient will set the
                      convergence threshold of the linear solve.


    RETURNS
    -------
    A dictionary storing each of these parameters.
    """
    return {"solver": "gmres", "n_krylov": n_krylov,
            "max_restarts": max_restarts, "tol_coef": tol_coef}