mparray.py 文件源码

python
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项目:mpnum 作者: dseuss 项目源码 文件源码
def _extract_factors(tens, ndims):
    """Extract iteratively the leftmost MPO tensor with given number of
    legs by a qr-decomposition

    :param np.ndarray tens: Full tensor to be factorized
    :param ndims: Number of physical legs per site or iterator over number of
        physical legs
    :returns: List of local tensors with given number of legs yielding a
        factorization of tens
    """
    current = next(ndims) if isinstance(ndims, collections.Iterator) else ndims
    if tens.ndim == current + 2:
        return [tens]
    elif tens.ndim < current + 2:
        raise AssertionError("Number of remaining legs insufficient.")
    else:
        unitary, rest = qr(tens.reshape((np.prod(tens.shape[:current + 1]), -1)))

        unitary = unitary.reshape(tens.shape[:current + 1] + rest.shape[:1])
        rest = rest.reshape(rest.shape[:1] + tens.shape[current + 1:])

        return [unitary] + _extract_factors(rest, ndims)
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