calculate total pressure at given volume and temperature

        :param v: unit-cell volume in A^3
        :param temp: temperature in K
        :return: pressure in GPa
        :note: 2017/05/10 temp must be numpy array.  If not, such as list,
            create an error.

def cal_p(self, v, temp):
        """
        calculate total pressure at given volume and temperature

        :param v: unit-cell volume in A^3
        :param temp: temperature in K
        :return: pressure in GPa
        :note: 2017/05/10 temp must be numpy array.  If not, such as list,
            create an error.
        """
        if not isinstance(temp, np.ndarray):
            temp = np.asarray(temp)
        if not isinstance(v, np.ndarray):
            v = np.asarray(v)
        return self.cal_pst(v) + self.cal_pth(v, temp) + \
            self.cal_pel(v, temp) + self.cal_panh(v, temp)