class_docstr: 将多个特征矩阵在channel维度进行concatenate拼接
class_docstr_tok: ["\u5c06\u591a\u4e2a\u7279\u5f81\u77e9\u9635\u5728channel\u7ef4\u5ea6\u8fdb\u884cconcatenate\u62fc\u63a5"]
code: def forward(self, x, outputs):
      return (
          torch.cat([outputs[i] for i in self.layers], 1)
          if self.multiple
          else outputs[self.layers[0]]
      )
  
imports: import torch.nn.functional
  from .utils import *
label_desc: Use image node_id 2 for calling the FeatureConcat obj's underlying member method code with example usage: obj.forward(x, outputs) and returns: unknown