maskrcnn_benchmark模型研究——modeling.backbone.fpn.py

         参数：

    
              x（list [Tensor]）：每个特征层的特征图。大概是Conv2~Conv5
    
         返回：
    
              results（tuple [Tensor]）：FPN图层后的特征图，大概是P2~P6  （在这里又加了一层）
    
                  它们是从最高分辨率开始排序的。 也就是＃P2〜P6
    
    
    
    

 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.

    
 import torch
    
 import torch.nn.functional as F
    
 from torch import nn
    
  
    
  
    
 class FPN(nn.Module):
    
     """
    
     Module that adds FPN on top of a list of feature maps.
    
     The feature maps are currently supposed to be in increasing