def reweight_drift(p, alt_i, delta_prob, a_go, a_no):
    """ update direct & indirect drift-rates for multirace winner
    """
    vd_exp = p['vd'][alt_i]
    vi_exp = p['vi'][alt_i]
    p['vd'][alt_i] = vd_exp + a_go * delta_prob
    p['vi'][alt_i] = vi_exp + a_no * -delta_prob
    return p
