code: def l2_norm(x):
      x = x**2
      x = x.sum(axis=[1, 2, 3], keepdim=True)
      return paddle.sqrt(x)
  
file_path: PaddleSeg/Matting/ppmatting/models/layers/gca_module.py
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddleseg.cvlibs import param_init
label_desc: Use image node_id 12 for calling the GuidedCxtAtten obj's underlying member method code with example usage: obj.l2_norm(x) and returns: paddle