<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def universal_anisotropy(self):
 """ returns the universal anisotropy value """

        return 5. * self.g_voigt / self.g_reuss + \
            self.k_voigt / self.k_reuss - 6.