Get Xmu from file.

        Args:
            xmu_dat_file (str): filename and path for xmu.dat
            feff_inp_file (str): filename and path of feff.inp input file

        Returns:
             Xmu object

def from_file(xmu_dat_file="xmu.dat", feff_inp_file="feff.inp"):
        """
        Get Xmu from file.

        Args:
            xmu_dat_file (str): filename and path for xmu.dat
            feff_inp_file (str): filename and path of feff.inp input file

        Returns:
             Xmu object
        """
        data = np.loadtxt(xmu_dat_file)
        header = Header.from_file(feff_inp_file)
        parameters = Tags.from_file(feff_inp_file)
        pots = Potential.pot_string_from_file(feff_inp_file)
        # site index (Note: in feff it starts from 1)
        if "RECIPROCAL" in parameters:
            absorbing_atom = parameters["TARGET"]
        # species symbol
        else:
            absorbing_atom = pots.splitlines()[3].split()[2]
        return Xmu(header, parameters, absorbing_atom, data)