stanfordnlp/CoreNLP · error · IllegalStateException

Unknown minimizer

Error message

Unknown minimizer: {minimizer}

What it means

KBPStatisticalExtractor.initFactory selects a qnMinimizer ('l1' or 'l2'); any other value hits the switch's default branch and throws IllegalStateException. This is a configuration check guarding the optimizer choice used when building the feature factory. The message includes the offending minimizer string.

Solutions

1. Set the minimizer property to exactly 'l1' or 'l2' (lowercase) in the properties used to build the factory.
2. Remove the minimizer property entirely to use the default branch behavior if unsure.
3. Check the CoreNLP version's supported minimizer strings in KBPStatanicalExtractor source if upgrading from an older release.

Example fix

// before
props.setProperty("minimizer", "L2");
// after
props.setProperty("minimizer", "l2");

String minimizer = props.getProperty("minimizer");
if (minimizer != null && !minimizer.equals("l1") && !minimizer.equals("l2")) {
  throw new IllegalArgumentException("minimizer must be 'l1' or 'l2', got: " + minimizer);
}

try {
  factory = KBPStatisticalExtractor.factory(props);
} catch (IllegalStateException e) {
  log.warn("Falling back to default minimizer: " + e.getMessage());
  props.remove("minimizer");
  factory = KBPStatisticalExtractor.factory(props);
}

When it happens

Trigger: Calling initFactory/factory with a properties object whose 'minimizer' (qnMinimizer) key is set to something other than 'l1' or 'l2', e.g. a typo like 'L2', 'lbfgs', or 'l-2'.

Common situations: Copying training config from docs of another CoreNLP version, hand-editing props files with wrong case ('L1' vs 'l1'), or passing an optimizer name from a different ML library.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Unknown clique: " + clique
• originalWords and sentence of different sizes…
• preTokenized option set: Non-standard annotators list…
• Unknown LogPriorType:
• unsupported language

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/4f6e68b79b067b99. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ie/KBPStatisticalExtractor.java:597

        factory.useHybridMinimizerWithInPlaceSGD(100, 1000, sigma);
        minimizerFactory = () -> {
          SGDMinimizer<DiffFunction> firstMinimizer = new SGDMinimizer<>(sigma, 50, 1000);
          QNMinimizer secondMinimizer = new QNMinimizer(15);
          return new HybridMinimizer(firstMinimizer, secondMinimizer, 50);
        };
        break;
      case L1:
        minimizerFactory = () -> {
          try {
            return MetaClass.create("edu.stanford.nlp.optimization.OWLQNMinimizer").createInstance(sigma);
          } catch (Exception e) {
            log.err("Could not create l1 minimizer! Reverting to l2.");
            return new QNMinimizer(15);
          }
        };
        break;
      default:
        throw new IllegalStateException("Unknown minimizer: " + minimizer);
    }
    factory.setMinimizerCreator(minimizerFactory);
    return factory;
  }


  /**
   * Train a multinomial classifier off of the provided dataset.
   * @param dataset The dataset to train the classifier off of.
   * @return A classifier.
   */
  public static Classifier<String, String> trainMultinomialClassifier(
      GeneralDataset<String, String> dataset,
      int featureThreshold,
      double sigma) {
    // Set up the dataset and factory
    log.info("Applying feature threshold (" + featureThreshold + ")...");
    dataset.applyFeatureCountThreshold(featureThreshold);

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