'Returns the log-transformed bounds on the theta.
Returns
bounds : array, shape (n_dims, 2)
The log-transformed bounds on the kernel\'s hyperparameters theta'

@property
def bounds(self):

    if (self.k1.bounds.size == 0):
        return self.k2.bounds
    if (self.k2.bounds.size == 0):
        return self.k1.bounds
    return np.vstack((self.k1.bounds, self.k2.bounds))
