def calculate_L(W, frequency, S):
    """
    Calculate L, which is subsequently used to perform rotational temperature analysis.

    Parameters
    ----------
    W - float
        Integrated flux of a line
    frequency - float
        Frequency of a transition in MHz
    S - float
        Intrinsic linestrength of the transition

    Returns
    -------
    L - float
    """
    L = (2.04e20 * W) / (S * frequency**3)
    return L