class_docstr: This `Module` represents a gated sum of two tensors `a` and `b`. Specifically:
  ```
  f = activation(W [a; b])
  out = f * a + (1 - f) * b
  ```
  
  # Parameters
  
  input_dim : `int`, required
      The dimensionality of the input. We assume the input have shape `(..., input_dim)`.
  activation : `Activation`, optional (default = `torch.nn.Sigmoid()`)
      The activation function to use.
code: def get_output_dim(self):
      return self.input_dim
  
file_path: allennlp/allennlp/modules/gated_sum.py
imports: import torch
  from allennlp.nn import Activation
label_desc: Use image node_id 3 for calling the GatedSum obj's underlying member method code with example usage: obj.get_output_dim() and returns: self