code: public SDVariable sigmoid(String name, SDVariable x) {
          validateFloatingPoint("sigmoid", x);
          SDVariable result = f().sigmoid(x);
          return updateVariableNameAndReference(result, name);
      }
docs: Element-wise sigmoid function: out[i] = 1.0/(1+exp(-in[i]))
  
  @param name Output variable name
  @param x    Input Variable
  @return Output variable