def init_r0_pulse(r, l, k):
    """calculate initial total RNA via ODE formula of RNA kinetics for one-shot/kinetics experiment

    Parameters
    ----------
        r:
            total RNA at current time point.
        l:
            labeled RNA at current time point.
        k:
            $k = 1 - e^{-\gamma t}$

    Returns
    -------
        r0:
            The intial total RNA at the beginning of the one-shot or kinetics experiment.
    """
    r0 = (r - l) / (1 - k)

    return r0