ratio of the input size, this option can be given. This has to
        be a number or tuple in the range (0, 1)
  * **return_indices** -- if "True", will return the indices along
    with the outputs. Useful to pass to "max_unpool2d()".

Examples::
      >>> input = torch.randn(20, 16, 50, 32)
      >>> # pool of square window of size=3, and target output size 13x12
      >>> F.fractional_max_pool2d(input, 3, output_size=(13, 12))
      >>> # pool of square window and target output size being half of input image size
      >>> F.fractional_max_pool2d(input, 3, output_ratio=(0.5, 0.5))