class_docstr: 使用全连接网络.
  
  参数:
      obs_dim (int): 观测空间的维度.
      act_dim (int): 动作空间的维度.
code: def forward(self, x):  # 可直接用 model = Model(5); model(obs)调用
      out = paddle.tanh(self.fc1(x))
      prob = F.softmax(self.fc2(out), axis=-1)
      return prob
  
file_path: PARL/examples/tutorials/parl2_dygraph/lesson4/policy_gradient/model.py
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  import parl
label_desc: Use image node_id 2 for calling the Model obj's underlying member method code with example usage: obj.forward(x) and returns: prob