typically call via setupz instead

def _ztanh(Np: int, gridmin: float, gridmax: float) -> np.ndarray:
    """
    typically call via setupz instead
    """
    x0 = np.linspace(0, 3.14, Np)  # arbitrarily picking 3.14 as where tanh gets to 99% of asymptote
    return np.tanh(x0)*gridmax+gridmin