def pdot_from_B(p, B):
    """
    pdot_from_B(p, B):
        Return a pdot (or p, actually) that a pulsar with spin
        period (or pdot) 'p' (in sec) would experience given a
        magnetic field strength 'B' in gauss.
    """
    return (B / 3.2e19)**2.0 / p