code: def forward(self, inputs_, down):
      x = F.interpolate(inputs_, scale_factor=self.scale_factor)
      x = torch.cat([x, down], dim=1)
  
      x1 = self.stack1(x)
      x3 = self.stack3(x)
      x5 = self.stack5(x)
      x_pool = self.stack_pool(x)
  
      x = torch.cat([x1, x3, x5, x_pool], dim=1)
      x = self.reducer(x)
  
      return x
  
imports: import torch
  import torch.nn
  import torch.nn.functional
label_desc: Use image node_id 2 for calling the UNetUpStack obj's underlying member method code with example usage: obj.forward(inputs_, down) and returns: x