It seems that activation.linear means forwarding without activation?
  

      github.com
  

  
    keras-team/keras/blob/5c4074a820a08505cf87562f60d21adfdc2dfb05/keras/activations.py#L459-L477



      
      
          @keras_export('keras.activations.linear')
          @tf.__internal__.dispatch.add_dispatch_support
          def linear(x):
            """Linear activation function (pass-through).
          
          
  For example:
          
          
  >>> a = tf.constant([-3.0,-1.0, 0.0,1.0,3.0], dtype = tf.float32)
            >>> b = tf.keras.activations.linear(a)
            >>> b.numpy()
            array([-3., -1.,  0.,  1.,  3.], dtype=float32)
          
          
  Args:
                x: Input tensor.
          
          
  Returns:
                The input, unmodified.
            """
            return x