/**
 * Alters the length normalization of the similarity as compared to DefaultSimilarity, but nothing else
 */
public class MySimilarity extends DefaultSimilarity {

  private static final float DEFAULT_NUMERATOR = 10.0f;
  private float numerator = DEFAULT_NUMERATOR;

  private static final double DEFAULT_DENOMINATOR_FACTOR = 99;
  private double denominatorFactor = DEFAULT_DENOMINATOR_FACTOR;

  public MySimilarity() {
  }


  /** A less steep length normalization method for document text fields,
   *  which gives very short less of an advantage.
   *  Implemented as <code>{numerator / sqrt(numTerms + denominatorFactor)}</code>.
   */
  @Override
  public float lengthNorm(FieldInvertState state) {
    return state.getBoost() * (float) (numerator / Math.sqrt(state.getLength() + denominatorFactor));
  }
}