output_size: the target output size of the image of the form D x H x W. Can be a tuple (D, H, W) or a single D for a cube D x D x D. D, H and W can be either a int, or None which means the size will be the same as that of the input.
return_indices: if TRUE, will return the indices along with the outputs. Useful to pass to nn_max_unpool3d(). Default: FALSE