code: def backward(ctx, dA: torch.Tensor) -> Tuple[None, torch.Tensor]:
      x, W, z1, z2 = ctx.saved_tensors
      _, K = x.shape
      K, N = W.shape
      dW = torch.empty(W.shape, device=x.device, dtype=x.dtype)
      # dA1 = torch.zeros((K, N // 2), device=x.device, dtype=x.dtype)
      # dA2 = torch.zeros((K, N // 2), device=x.device, dtype=x.dtype)
      dz1 = torch.zeros((K, N // 2), device=x.device, dtype=x.dtype)
      dz2 = torch.zeros((K, N // 2), device=x.device, dtype=x.dtype)
      assert dz1.T.shape[1] == x.shape[0]
      assert dz1.T.shape == dz2.T.shape
      P, Q = dz1.T.shape
      Q, R = x.shape
      dW = torch.zeros(R, P * 2, device=x.device, dtype=x.dtype)
  
      grid = lambda meta: (
          triton.cdiv(dz1.numel(), meta["BLOCK_SIZE"]),
      )
      gelu_partial_layer_fused_backward[grid](  # type: ignore
          z1, z2, dA, dz1, dz2, BLOCK_SIZE=512
      )
      grid = lambda META: (
          triton.cdiv(P, META["BLOCK_SIZE_P"])
          * triton.cdiv(R, META["BLOCK_SIZE_R"]),
      )
      gelu_partial_layer_fused_backward_matmul[grid](  # type: ignore
          dz1,
          x,
          dz2,
          dW,
          P,
          R,
          Q,
          dz1.T.stride(0),
          dz1.T.stride(1),
          x.stride(0),
          x.stride(1),
          dW.stride(0) // 2,
          dW.stride(1),
          BLOCK_SIZE_P=32,  # type: ignore
          BLOCK_SIZE_R=32,  # type: ignore
          BLOCK_SIZE_Q=16,  # type: ignore
          GROUP_SIZE_P=8,  # type: ignore
      )
      # TODO: Remove for production. This is for debugging only:
      # Store the outputs to compare to pytorch
      # global triton_dA1
      # global triton_dA2
      # global triton_dz1
      # global triton_dz2
      global triton_dW
      # triton_dA1 = dA1
      # triton_dA2 = dA2
      # triton_dz1 = dz1
      # triton_dz2 = dz2
      triton_dW = dW
      return None, dW
  
imports: from typing import Tuple
  import torch
  import triton
  import triton.language
  import numpy
label_desc: Use image node_id 2 for calling the PartialGeluLayer obj's underlying member method code with example usage: obj.backward(ctx, dA) and returns: None,  dW