def Fierz_to_Bern_chrom(C, dd, parameters):
    """From Fierz to chromomagnetic Bern basis for Class V.
    dd should be of the form 'sb', 'ds' etc."""
    e = sqrt(4 * pi * parameters['alpha_e'])
    gs = sqrt(4 * pi * parameters['alpha_s'])
    if dd == 'sb' or dd == 'db':
        mq = parameters['m_b']
    elif dd == 'ds':
        mq = parameters['m_s']
    else:
        KeyError("Not sure what to do with quark mass for flavour {}".format(dd))
    return {
        '7gamma' + dd : gs**2 / e / mq * C['F7gamma' + dd ],
        '8g' + dd : gs / mq * C['F8g' + dd ],
        '7pgamma' + dd : gs**2 / e /mq * C['F7pgamma' + dd],
        '8pg' + dd : gs / mq * C['F8pg' + dd]
            }
From Fierz to chromomagnetic Bern basis for Class V.
    dd should be of the form 'sb', 'ds' etc.