factory.py 文件源码

def _random_state(sites, ldim, randstate=None):
    """Returns a random positive semidefinite operator of shape (ldim, ldim) *
    sites normalized to Tr rho = 1, i.e. a mixed state with local dimension
    `ldim` living on `sites` sites. Note that the returned state is positive
    semidefinite only when interpreted in global form (see
    :func:`tools.global_to_local`)

    :param sites: Number of local sites
    :param ldim: Local ldimension
    :param randstate: numpy.random.RandomState instance or None
    :returns: numpy.ndarray of shape (ldim, ldim) * sites

    >>> from numpy.linalg import eigvalsh
    >>> rho = _random_state(3, 2).reshape((2**3, 2**3))
    >>> all(eigvalsh(rho) >= 0)
    True
    >>> np.abs(np.trace(rho) - 1) < 1e-6
    True
    """
    shape = (ldim**sites, ldim**sites)
    mat = _zrandn(shape, randstate=randstate)
    rho = np.conj(mat.T).dot(mat)
    rho /= np.trace(rho)
    return rho.reshape((ldim,) * 2 * sites)


####################################
#  Factory functions for MPArrays  #
####################################