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package org.openscience.cdk.similarity;

import org.openscience.cdk.annotations.TestClass;
import org.openscience.cdk.annotations.TestMethod;
import org.openscience.cdk.exception.CDKException;

import Java.util.BitSet;

/**
 *  Calculates the Tanimoto coefficient for a given pair of two
 *  fingerprint bitsets or real valued feature vectors.
 *
 *  The Tanimoto coefficient is one way to
 *  quantitatively measure the "distance" or similarity of
 *  two chemical structures.
 *
 *  <p>You can use the FingerPrinter class to retrieve two fingerprint bitsets.
 *  We assume that you have two structures stored in cdk.Molecule objects.
 *  A tanimoto coefficient can then be calculated like:
 *  <pre>
 *   BitSet fingerprint1 = Fingerprinter.getFingerprint(molecule1);
 *   BitSet fingerprint2 = Fingerprinter.getFingerprint(molecule2);
 *   float tanimoto_coefficient = Tanimoto.calculate(fingerprint1, fingerprint2);
 *  </pre>
 *
 *  <p>The FingerPrinter assumes that hydrogens are explicitely given, if this
 *  is desired!
 *  <p>Note that the continuous Tanimoto coefficient does not lead to a metric space
 *
 *@author         steinbeck
 * @cdk.githash
 *@cdk.created    2005-10-19
 *@cdk.keyword    jaccard
 *@cdk.keyword    similarity, tanimoto
 * @cdk.module fingerprint
 */
@TestClass("org.openscience.cdk.similarity.TanimotoTest")
public class Tanimoto
{

    /**
     * Evaluates Tanimoto coefficient for two bit sets.
     *
     * @param bitset1 A bitset (such as a fingerprint) for the first molecule
     * @param bitset2 A bitset (such as a fingerprint) for the second molecule
     * @return The Tanimoto coefficient
     * @throws org.openscience.cdk.exception.CDKException  if bitsets are not of the same length
     */
    @TestMethod("testTanimoto1,testTanimoto2")
    public static float calculate(BitSet bitset1, BitSet bitset2) throws CDKException
    {
        float _bitset1_cardinality = bitset1.cardinality();
        float _bitset2_cardinality = bitset2.cardinality();
        if (bitset1.size() != bitset2.size()) {
            throw new CDKException("Bisets must have the same bit length");
        }
        BitSet one_and_two = (BitSet)bitset1.clone();
        one_and_two.and(bitset2);
        float _common_bit_count = one_and_two.cardinality();
        return _common_bit_count/(_bitset1_cardinality + _bitset2_cardinality - _common_bit_count);
    }
   
    /**
     * Evaluates the continuous Tanimoto coefficient for two real valued vectors.
     *
     * @param features1 The first feature vector
     * @param features2 The second feature vector
     * @return The continuous Tanimoto coefficient
     * @throws org.openscience.cdk.exception.CDKException  if the features are not of the same length
     */
    @TestMethod("testTanimoto3")
    public static float calculate(double[] features1, double[] features2) throws CDKException {

        if (features1.length != features2.length) {
            throw new CDKException("Features vectors must be of the same length");
        }

        int n = features1.length;
        double ab = 0.0;
        double a2 = 0.0;
        double b2 = 0.0;

        for (int i = 0; i < n; i++) {
            ab += features1[i] * features2[i];
            a2 += features1[i]*features1[i];
            b2 += features2[i]*features2[i];
        }
        return (float)ab/(float)(a2+b2-ab);
    }
}

通过源码可以看出calculate(BitSet bitset1, BitSet bitset2)方法,是通过比较两个分子的fingerprint的位,来计算相似度.通过BitSet的and操作得到共同的个数,然后在除以总共为true的个数,这样就得到相似值.