def tburst_from_fage(tage=0.0, fage_burst=0.0, **extras):
    """This function transfroms from a fractional age of a burst to an absolute
    age.  With this transformation one can sample in ``fage_burst`` without
    worry about the case ``tburst`` > ``tage``.

    Parameters
    ----------
    tage : float, Gyr
        The age of the host galaxy.

    fage_burst : float between 0 and 1
        The fraction of the host age at which the burst occurred.

    Returns
    -------
    tburst : float, Gyr
        The age of the host when the burst occurred (i.e. the FSPS ``tburst``
        parameter)
    """
    return tage * fage_burst