def set_calculator(eos_mod, kind, kind_opts):
    assert kind in kind_opts, (
        kind + ' is not a valid thermal calculator. '+
        'You must select one of: ' +  str(kind_opts))

    eos_mod._kind = kind

    if   kind=='GammaPowLaw':
        calc = _GammaPowLaw(eos_mod)
    elif kind=='GammaShiftPowLaw':
        calc = _GammaShiftPowLaw(eos_mod)
    elif kind=='GammaFiniteStrain':
        calc = _GammaFiniteStrain(eos_mod)
    else:
        raise NotImplementedError(kind+' is not a valid '+
                                  'GammaEos Calculator.')

    eos_mod._add_calculator(calc, calc_type='gamma')
    pass