docs: def Flavio_to_Fierz_chrom(C, qq, parameters):
      """From Flavio to chromomagnetic Fierz basis for Class V.
      qq should be of the form 'sb', 'db' etc."""
      p = parameters
      V = ckmutil.ckm.ckm_tree(p["Vus"], p["Vub"], p["Vcb"], p["delta"])
      if qq == 'sb':
          xi = V[2, 2] * V[2, 1].conj()
      elif qq == 'db':
          xi = V[2, 2] * V[2, 0].conj()
      elif qq == 'ds':
          xi = V[2, 1] * V[2, 0].conj()
      elif qq == 'uc':
          xi = V[1, 2].conj() * V[0, 2]
      else:
          raise ValueError("Unexpected flavours: {}".format(qq))
      qqfl = qq[::-1]
      e = sqrt(4 * pi * parameters['alpha_e'])
      gs = sqrt(4 * pi * parameters['alpha_s'])
      if qq == 'sb' or qq == 'db':
          mq = parameters['m_b']
      elif qq == 'ds':
          mq = parameters['m_s']
      elif qq == 'uc':
          mq = parameters['m_c']
      else:
          KeyError("Not sure what to do with quark mass for flavour {}".format(qq))
      dic = {
          'F7gamma' + qq: C["C7_" + qqfl] / ((16 * pi**2) / e / mq),
          'F8g' + qq: C["C8_" + qqfl] / ((16 * pi**2) / gs / mq),
          'F7pgamma' + qq: C["C7p_" + qqfl] / ((16 * pi**2) / e / mq),
          'F8pg' + qq: C["C8p_" + qqfl] / ((16 * pi**2) / gs / mq)
              }
      prefactor = sqrt(2)/p['GF']/xi/4
      return {k: v / prefactor for k, v in dic.items()}