code: def gather(comm, x, root=0):
      """Differentiable gather communication between workers.
  
      This function invokes gather communications among processes specified
      by the communicator. Backward will be invoked as well as the ordinary
      chainer functions, where gradients are scattered from the root process
      to each slave.
  
      The received array will be on the current CUDA device if ``x`` on the
      root process is on GPU. Please be aware that the current CUDA device
      is intended one.
      (``https://docs-cupy.chainer.org/en/stable/tutorial/basic.html#current-device``)
  
      Args:
          comm: ChainerMN communicator.
          x (chainer.Variable): Variable to be sent.
  
      Returns:
          ys (chainer.Variable):
              Gathered variables. ``None`` for slaves.
      """
      chainer.utils.experimental("chainermn.functions.gather")
  
      return Gather(comm, root)(x)
  
imports: import chainer
  from chainer import backend
  import numpy
label_desc: Use image node_id 4 for calling a global function with example usage: gather(comm, x, root) and returns: Gather