linalg.py 文件源码

def fl2norm2(xf, axis=(0, 1)):
    r"""
    Compute the squared :math:`\ell_2` norm in the DFT domain, taking
    into account the unnormalised DFT scaling, i.e. given the DFT of a
    multi-dimensional array computed via :func:`fftn`, return the
    squared :math:`\ell_2` norm of the original array.

    Parameters
    ----------
    xf : array_like
      Input array
    axis : sequence of ints, optional (default (0,1))
      Axes on which the input is in the frequency domain

    Returns
    -------
    x : float
      :math:`\|\mathbf{x}\|_2^2` where the input array is the result of
      applying :func:`fftn` to the specified axes of multi-dimensional
      array :math:`\mathbf{x}`
    """

    xfs = xf.shape
    return (linalg.norm(xf)**2)/np.prod(np.array([xfs[k] for k in axis]))