<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def precision_matrix(self):
 """ Returns the precision matrix of the distribution. Precision is defined as the inverse of the variance. This method returns the inverse matrix of the covariance. Examples -------- array([[ 0.3125 , -0.125 , 0. ], [-0.125 , 0.58333333, 0.33333333], [ 0. , 0.33333333, 0.33333333]]) """

        if self._precision_matrix is None:
            self._precision_matrix = np.linalg.inv(self.covariance)
        return self._precision_matrix