code: def down_sampling(self, in_channels, out_channels):
      modules = []
      modules.append(nn.MaxPool2D(kernel_size=2, stride=2))
      modules.append(layers.ConvBNReLU(in_channels, out_channels, 3))
      modules.append(layers.ConvBNReLU(out_channels, out_channels, 3))
      return nn.Sequential(*modules)
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddleseg import utils
  from paddleseg.cvlibs import manager
  from paddleseg.models import layers
label_desc: Use image node_id 2 for calling the Encoder obj's underlying member method code with example usage: obj.down_sampling(in_channels, out_channels) and returns: nn