def joint_membership(a, b):
    """Calculate the joint membership of arrays.

    Parameters
    ----------
    a : array-like of shape (n_samples,)
        The first array of membership.
    b : array-like of shape (n_samples,)
        The second array of membership.

    Returns
    -------
    joint_membership_ : array-like of float of shape (n_samples,)
        The joint membership of a and b.
    """
    joint_membership_ = a * b

    return joint_membership_