def to_molar_ratio(massfrac_numerator, massfrac_denominator, numerator_mass, denominator_mass):
return (massfrac_numerator / numerator_mass) / (massfrac_denominator / denominator_mass)<EOL>
Converts per-mass concentrations to molar elemental ratios.

Be careful with units.

Parameters
----------
numerator_mass, denominator_mass : float or array-like
    The atomic mass of the numerator and denominator.
massfrac_numerator, massfrac_denominator : float or array-like
    The per-mass fraction of the numnerator and denominator.

Returns
-------
float or array-like : The molar ratio of elements in the material