factory.py 文件源码

def random_mpo(sites, ldim, rank, randstate=None, hermitian=False,
               normalized=True, force_rank=False):
    """Returns an hermitian MPO with randomly choosen local tensors

    :param sites: Number of sites
    :param ldim: Local dimension
    :param rank: Rank
    :param randstate: numpy.random.RandomState instance or None
    :param hermitian: Is the operator supposed to be hermitian
    :param normalized: Operator should have unit norm
    :param force_rank: If True, the rank is exaclty `rank`.
        Otherwise, it might be reduced if we reach the maximum sensible rank.
    :returns: randomly choosen matrix product operator

    >>> mpo = random_mpo(4, 2, 10, force_rank=True)
    >>> mpo.ranks, mpo.shape
    ((10, 10, 10), ((2, 2), (2, 2), (2, 2), (2, 2)))
    >>> mpo.canonical_form
    (0, 4)

    """
    mpo = random_mpa(sites, (ldim,) * 2, rank, randstate=randstate,
                     force_rank=force_rank, dtype=np.complex_)

    if hermitian:
        # make mpa Herimitan in place, without increasing rank:
        ltens = (l + l.swapaxes(1, 2).conj() for l in mpo.lt)
        mpo = mp.MPArray(ltens)
    if normalized:
        # we do this with a copy to ensure the returned state is not
        # normalized
        mpo /= mp.norm(mpo.copy())

    return mpo