def fp(v, g, x):
    """FP-neuron function, as described in Equation 7 in the Paper.

    Parameters
    ----------
    v : np.array
        filter vector 1
    g : np.array
        filter vector 2
    x : np.array
        position

    Returns
    -------
    float
        function value
    """
    sp_vx = (v * x).sum(-1)
    sp_gx = (g * x).sum(-1)
    return sp_vx * sp_gx