code: public OutputVariable getOutputVariable(String name) {
          for (OutputVariable outputVariable : this.outputVariables) {
              if (outputVariable.getName().equals(name)) {
                  return outputVariable;
              }
          }
          throw new RuntimeException(String.format(
                  "[engine error] no output variable by name <%s>", name));
      }
docs: Gets the output variable of the given name after iterating the output
  variables. The cost of this method is O(n), where n is the number of output
  variables in the engine. For performance, please get the variables by
  index.
  
  @param name is the name of the output variable
  @return output variable of the given name
  @throws RuntimeException if there is no variable with the given name