class_docstr: A downsampling layer with an optional convolution.
  :param channels: channels in the inputs and outputs.
  :param use_conv: a bool determining if a convolution is applied.
  :param dims: determines if the signal is 1D, 2D, or 3D. If 3D, then
               downsampling occurs in the inner-two dimensions.
class_docstr_tok: ["A","downsampling","layer","with","an","optional","convolution",".",":","param","channels",":","channels","in","the","inputs","and","outputs",".",":","param","use_conv",":","a","bool","determining","if","a","convolution","is","applied",".",":","param","dims",":","determines","if","the","signal","is","1D",",","2D",",","or","3D",".","If","3D",",","then","downsampling","occurs","in","the","inner-two","dimensions","."]
code: def forward(self, x):
      assert x.shape[1] == self.channels
      return self.op(x)
  
imports: import math
  from abc import abstractmethod
  import numpy
  import torch
  import torch.nn
  import torch.nn.functional
  from ldm.modules.attention import SpatialTransformer
  from ldm.modules.diffusionmodules.util import avg_pool_nd, checkpoint, conv_nd, linear, normalization, timestep_embedding, zero_module
  from ldm.util import exists
label_desc: Use image node_id 2 for calling the Downsample obj's underlying member method code with example usage: obj.forward(x) and returns: self