Package org.apache.lucene.index

Enum VectorSimilarityFunction

  • All Implemented Interfaces:
    Serializable, Comparable<VectorSimilarityFunction>
    public enum VectorSimilarityFunction
extends Enum<VectorSimilarityFunction>
    Vector similarity function; used in search to return top K most similar vectors to a target vector. This is a label describing the method used during indexing and searching of the vectors in order to determine the nearest neighbors.

    • Enum Constant Detail

      • DOT_PRODUCT

        public static final VectorSimilarityFunction DOT_PRODUCT
        Dot product. NOTE: this similarity is intended as an optimized way to perform cosine similarity. In order to use it, all vectors must be of unit length, including both document and query vectors. Using dot product with vectors that are not unit length can result in errors or poor search results.

      • COSINE

        public static final VectorSimilarityFunction COSINE
        Cosine similarity. NOTE: the preferred way to perform cosine similarity is to normalize all vectors to unit length, and instead use DOT_PRODUCT. You should only use this function if you need to preserve the original vectors and cannot normalize them in advance.

    • Field Detail

      • reversed

        public final boolean reversed
        If true, the scores associated with vector comparisons are nonnegative and in reverse order; that is, lower scores represent more similar vectors. Otherwise, if false, higher scores represent more similar vectors, and scores may be negative or positive.

    • Method Detail

      • values

        public static VectorSimilarityFunction[] values()
        Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows: 
        for (VectorSimilarityFunction c : VectorSimilarityFunction.values())
    System.out.println(c);
        Returns:
        an array containing the constants of this enum type, in the order they are declared

      • valueOf

        public static VectorSimilarityFunction valueOf​(String name)
        Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)
        Parameters:
        name - the name of the enum constant to be returned.
        Returns:
        the enum constant with the specified name
        Throws:
        IllegalArgumentException - if this enum type has no constant with the specified name
        NullPointerException - if the argument is null

      • compare

        public abstract float compare​(float[] v1,
                              float[] v2)
        Calculates a similarity score between the two vectors with a specified function.
        Parameters:
        v1 - a vector
        v2 - another vector, of the same dimension
        Returns:
        the value of the similarity function applied to the two vectors

      • convertToScore

        public abstract float convertToScore​(float similarity)
        Converts similarity scores used (may be negative, reversed, etc) into document scores, which must be positive, with higher scores representing better matches.
        Parameters:
        similarity - the raw internal score as returned by compare(float[], float[]).
        Returns:
        normalizedSimilarity