code: public void restart() {
          for (InputVariable inputVariable : this.inputVariables) {
              inputVariable.setValue(Double.NaN);
          }
          for (OutputVariable outputVariable : this.outputVariables) {
              outputVariable.clear();
          }
      }
docs: Restarts the engine by setting the values of the input variables to fl::nan
  and clearing the output variables
  
  @see Variable::setValue()
  @see OutputVariable::clear()