def delete(self, doc):
        if doc.id is None:
            raise DatabaseException('Document does not have id')
        if doc.sid is None:
            try:
                rs = self.db.docs.remove({'id': doc.id}, safe=True)
                assert rs['n'] == 1
            except Exception as e:
                raise DatabaseException(e)
            return None
        doc.data = None
        return self.update(doc)
def phasor(bch, ax=0):
    """create phasor plot from bch"""
    f1 = bch.machine['p']*bch.dqPar['speed']
    w1 = 2*np.pi*f1
    xd = w1*bch.dqPar['ld'][-1]
    xq = w1*bch.dqPar['lq'][-1]
    r1 = bch.machine['r1']
    i1beta_phasor(bch.dqPar['up'][-1],
                  bch.dqPar['i1'][-1], bch.dqPar['beta'][-1],
                  r1, xd, xq, ax)