sum_leafs_along_axes
====================

.. py:function:: t3toolbox.backend.stacking.sum_leafs_along_axes(S, axes)

   .. code-block:: python

      def sum_leafs_along_axes(
              S,                              # tree of NDArrays (or single NDArray)
              axes: typ.Union[int, typ.Tuple[int, ...]],  # array axes summed in every leaf
      ):


   Sum leafs of a tree of NDArrays along specified axes.

   .. rubric:: Examples

   >>> import numpy as np
   >>> import t3toolbox.backend.stacking as stacking
   >>> A = np.ones((1,2,3,4))
   >>> B = np.ones((9,8,7,6,5))
   >>> C = np.ones((6,7,6,9))
   >>> S = (A, (B,C))
   >>> T = stacking.sum_leafs_along_axes(S, (1,3))
   >>> (A2, (B2, C2)) = T
   >>> print(np.linalg.norm(np.sum(A, axis=(1,3)) - A2))
   0.0
   >>> print(np.linalg.norm(np.sum(B, axis=(1,3)) - B2))
   0.0
   >>> print(np.linalg.norm(np.sum(C, axis=(1,3)) - C2))
   0.0