private function addCustomVariables(Model $model, $numberOfVarsToAdd, OutputInterface $output)
 {
     for ($index = 0; $index < $numberOfVarsToAdd; $index++) {
         $indexAdded = $model->addCustomVariable();
         $this->progress->advance();
         $output->writeln('  <info>Added a variable in scope "' . $model->getScopeName() . '" having the index ' . $indexAdded . '</info>');
     }
 }