def backwardFirst(self, dout, z):
    dw = dout.dot(z.T)
    db = np.sum(dout, axis=1)
    db = np.reshape(db, (db.shape[0], 1))
    return (dw, db)
def backwardFirst(self, dout, z):
    dw = dout.dot(z.T)
    db = np.sum(dout, axis=1)
    db = np.reshape(db, (db.shape[0], 1))
    return (dw, db)