def linear(I,w):
    """ 
    This is the Linear Kernel for External Current defined by:

    .. math::
        I(t+1) =I(t) + wI(t)

    :param I: External current.
    :type I: int, float or numpy.ndarray
    :param w: weight of the input current.
    :type w: int, float or numpy.ndarray
    """

    return I+w*I