def _get_param_size_str(m, n, alpha, beta, eta=None, eps=None):
    """Helper for creating string of problem size and parameters for
    plot titles.
    """
    size_str = fr'Size: $m={m}, n={n}$'
    param_str = fr'Parameters: $\alpha={alpha}, \beta={beta}'

    if eta is not None:
        param_str += fr', \eta={eta}$'

    if eps is not None:
        param_str += fr', \epsilon={eps}$'

    return '\n' + size_str + '\n' + param_str