'Pulls off the imuplse response coefficients to a shock
in :math:`w_{t}` for :math:`x` and :math:`y`
Important to note: We are uninterested in the shocks to
v for this method
* :math:`x` coefficients are :math:`C, AC, A^2 C...`
* :math:`y` coefficients are :math:`GC, GAC, GA^2C...`
Parameters
j : Scalar(int)
Number of coefficients that we want
Returns
xcoef : list(array_like(float, 2))
The coefficients for x
ycoef : list(array_like(float, 2))
The coefficients for y'

def impulse_response(self, j=5):

    (A, C, G, H) = (self.A, self.C, self.G, self.H)
    Apower = np.copy(A)
    xcoef = [C]
    ycoef = [np.dot(G, C)]
    for i in range(j):
        xcoef.append(np.dot(Apower, C))
        ycoef.append(np.dot(G, np.dot(Apower, C)))
        Apower = np.dot(Apower, A)
    return (xcoef, ycoef)
