def nm2lt7(short_nm: float, long_nm: float, step_cminv: float = <NUM_LIT:20>) -> Tuple[float, float, float]:
short = <NUM_LIT> / short_nm<EOL>long = <NUM_LIT> / long_nm<EOL>N = int(np.ceil((short-long) / step_cminv)) + <NUM_LIT:1>  <EOL>return short, long, N<EOL>
converts wavelength in nm to cm^-1
    minimum meaningful step is 20, but 5 is minimum before crashing lowtran

    short: shortest wavelength e.g. 200 nm
    long: longest wavelength e.g. 30000 nm
    step: step size in cm^-1 e.g. 20

    output in cm^-1