How to use the pyansys._binary_reader.compute_principal_stress function in pyansys

etype, ele_data_arr,
                                               nitem, elemtype,
                                               ptr_off,
                                               as_global=not in_element_coord_sys)

            if nitem != 6:
                ele_data_arr = ele_data_arr[:, :6]

        else:
            raise NotImplementedError('Not implemented for ANSYS older than v14.5')

        # trim off extra data
        ele_data_arr = ele_data_arr[:nelemnode]

        if principal:
            ele_data_arr, isnan = _binary_reader.compute_principal_stress(ele_data_arr)
            ele_data_arr[isnan] = np.nan

        splitind = np.cumsum(nnode)
        element_stress = np.split(ele_data_arr, splitind[:-1])

        # reorder list using sorted indices
        enum = self._eeqv
        sidx = np.argsort(enum)
        element_stress = [element_stress[i] for i in sidx]

        enode = []
        for i in sidx:
            enode.append(self.geometry.elem[i][10:10+nnode[i]])

        # Get element numbers
        elemnum = self._eeqv[self._sidx_elem]

>>> import pyansys
        >>> rst = pyansys.read_binary('file.rst')
        >>> nnum, stress = rst.principal_nodal_stress(0)

        Notes
        -----
        ANSYS equivalent of:
        PRNSOL, S, PRIN

        which returns:
        S1, S2, S3 principal stresses, SINT stress intensity, and SEQV
        equivalent stress.
        """
        # get component stress
        nodenum, stress = self.nodal_stress(rnum)
        pstress, isnan = _binary_reader.compute_principal_stress(stress)
        pstress[isnan] = np.nan
        return nodenum, pstress

pstress[isnan] = np.nan
            pstress_r, isnan = _binary_reader.compute_principal_stress(stress_r)
            pstress_r[isnan] = np.nan

            return nnum, pstress + 1j*pstress_r

        elif full_rotor:
            # compute principle stress
            pstress = np.empty((self.n_sector, stress.shape[1], 5), np.float64)
            for i in range(stress.shape[0]):
                pstress[i], isnan = _binary_reader.compute_principal_stress(stress[i])
                pstress[i, isnan] = np.nan
            return nnum, pstress

        else:
            pstress, isnan = _binary_reader.compute_principal_stress(stress)
            pstress[isnan] = np.nan
            return nnum, pstress

equivalent stress.
        """
        if as_complex and full_rotor:
            raise Exception('complex and full_rotor cannot both be True')

        # get component stress
        nnum, stress = self.nodal_stress(rnum, phase, as_complex, full_rotor)

        # compute principle stress
        if as_complex:
            stress_r = np.imag(stress)
            stress = np.real(stress)

            pstress, isnan = _binary_reader.compute_principal_stress(stress)
            pstress[isnan] = np.nan
            pstress_r, isnan = _binary_reader.compute_principal_stress(stress_r)
            pstress_r[isnan] = np.nan

            return nnum, pstress + 1j*pstress_r

        elif full_rotor:
            # compute principle stress
            pstress = np.empty((self.n_sector, stress.shape[1], 5), np.float64)
            for i in range(stress.shape[0]):
                pstress[i], isnan = _binary_reader.compute_principal_stress(stress[i])
                pstress[i, isnan] = np.nan
            return nnum, pstress

        else:
            pstress, isnan = _binary_reader.compute_principal_stress(stress)
            pstress[isnan] = np.nan
            return nnum, pstress

which returns:
        S1, S2, S3 principal stresses, SINT stress intensity, and SEQV
        equivalent stress.
        """
        if as_complex and full_rotor:
            raise Exception('complex and full_rotor cannot both be True')

        # get component stress
        nnum, stress = self.nodal_stress(rnum, phase, as_complex, full_rotor)

        # compute principle stress
        if as_complex:
            stress_r = np.imag(stress)
            stress = np.real(stress)

            pstress, isnan = _binary_reader.compute_principal_stress(stress)
            pstress[isnan] = np.nan
            pstress_r, isnan = _binary_reader.compute_principal_stress(stress_r)
            pstress_r[isnan] = np.nan

            return nnum, pstress + 1j*pstress_r

        elif full_rotor:
            # compute principle stress
            pstress = np.empty((self.n_sector, stress.shape[1], 5), np.float64)
            for i in range(stress.shape[0]):
                pstress[i], isnan = _binary_reader.compute_principal_stress(stress[i])
                pstress[i, isnan] = np.nan
            return nnum, pstress

        else:
            pstress, isnan = _binary_reader.compute_principal_stress(stress)

if as_complex:
            stress_r = np.imag(stress)
            stress = np.real(stress)

            pstress, isnan = _binary_reader.compute_principal_stress(stress)
            pstress[isnan] = np.nan
            pstress_r, isnan = _binary_reader.compute_principal_stress(stress_r)
            pstress_r[isnan] = np.nan

            return nnum, pstress + 1j*pstress_r

        elif full_rotor:
            # compute principle stress
            pstress = np.empty((self.n_sector, stress.shape[1], 5), np.float64)
            for i in range(stress.shape[0]):
                pstress[i], isnan = _binary_reader.compute_principal_stress(stress[i])
                pstress[i, isnan] = np.nan
            return nnum, pstress

        else:
            pstress, isnan = _binary_reader.compute_principal_stress(stress)
            pstress[isnan] = np.nan
            return nnum, pstress