code: public SDVariable gelu(String name, SDVariable x) {
          validateFloatingPoint("gelu", x);
          SDVariable ret = f().gelu(x, false);    //Defaults to si
          return updateVariableNameAndReference(ret, name);
      }
docs: GELU activation function - Gaussian Error Linear Units<br>
  For more details, see <i>Gaussian Error Linear Units (GELUs)</i> - <a href="https://arxiv.org/abs/1606.08415">https://arxiv.org/abs/1606.08415</a>
  This method uses the sigmoid approximation
  
  @param name Name of the output variable. May be null.
  @param x    Input
  @return Output variable - GELU applied to the input