class_docstr: Apply sum pooling over the nodes in the graph.
  
  .. math::
      r^{(i)} = \sum_{k=1}^{N_i} x^{(i)}_k
code: def __init__(self):
      super(SumPooling, self).__init__()
  
imports: from mxnet import gluon, nd
  from mxnet.gluon import nn
  from ...readout import broadcast_nodes, max_nodes, mean_nodes, softmax_nodes, sum_nodes, topk_nodes
label_desc: Use image node_id 1 to create a new SumPooling object from inherited base classes: nn with example: obj = SumPooling()