def receptive_field_pool(kernel, n0=1, shift_n=0, n_lyrs=1):
    """
    Compute receptive field for pooling layers

    Parameters
    ----------
    kernel
        kernel size
    n0
        receptive field from previous layer
    shift_n
        number of shifting pixels in shift convolution architecture
    n_lyrs
        number of layers

    Returns
    -------
    a tuple of two n1, s
    """
    n1 = n0 * kernel**n_lyrs
    if shift_n > 1:  # shift_n is the Nst pooling lyr
        s = 1 + 2**shift_n
    else:
        s = shift_n
    return n1, s