def liujordan(zenith, transmittance, airmass, dni_extra=<NUM_LIT>):
tau = transmittance<EOL>dni = dni_extra*tau**airmass<EOL>dhi = <NUM_LIT> * (<NUM_LIT:1.0> - tau**airmass) * dni_extra * np.cos(np.radians(zenith))<EOL>ghi = dhi + dni * np.cos(np.radians(zenith))<EOL>irrads = OrderedDict()<EOL>irrads['<STR_LIT>'] = ghi<EOL>irrads['<STR_LIT>'] = dni<EOL>irrads['<STR_LIT>'] = dhi<EOL>if isinstance(ghi, pd.Series):<EOL><INDENT>irrads = pd.DataFrame(irrads)<EOL><DEDENT>return irrads<EOL>
Determine DNI, DHI, GHI from extraterrestrial flux, transmittance,
and optical air mass number.

Liu and Jordan, 1960, developed a simplified direct radiation model.
DHI is from an empirical equation for diffuse radiation from Liu and
Jordan, 1960.

Parameters
----------
zenith: pd.Series
    True (not refraction-corrected) zenith angles in decimal
    degrees. If Z is a vector it must be of the same size as all
    other vector inputs. Z must be >=0 and <=180.

transmittance: float
    Atmospheric transmittance between 0 and 1.

pressure: float, default 101325.0
    Air pressure

dni_extra: float, default 1367.0
    Direct irradiance incident at the top of the atmosphere.

Returns
-------
irradiance: DataFrame
    Modeled direct normal irradiance, direct horizontal irradiance,
    and global horizontal irradiance in W/m^2

References
----------
[1] Campbell, G. S., J. M. Norman (1998) An Introduction to
Environmental Biophysics. 2nd Ed. New York: Springer.

[2] Liu, B. Y., R. C. Jordan, (1960). "The interrelationship and
characteristic distribution of direct, diffuse, and total solar
radiation".  Solar Energy 4:1-19