pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / src / java / org / apache / lucene / search / DefaultSimilarity.java

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/search/DefaultSimilarity.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/search/DefaultSimilarity.java
new file mode 100644 (file)
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+++ b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/search/DefaultSimilarity.java
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+package org.apache.lucene.search;
+
+import org.apache.lucene.index.FieldInvertState;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/** Expert: Default scoring implementation. */
+public class DefaultSimilarity extends Similarity {
+
+  /** Implemented as
+   *  <code>state.getBoost()*lengthNorm(numTerms)</code>, where
+   *  <code>numTerms</code> is {@link FieldInvertState#getLength()} if {@link
+   *  #setDiscountOverlaps} is false, else it's {@link
+   *  FieldInvertState#getLength()} - {@link
+   *  FieldInvertState#getNumOverlap()}.
+   *
+   *  @lucene.experimental */
+  @Override
+  public float computeNorm(String field, FieldInvertState state) {
+    final int numTerms;
+    if (discountOverlaps)
+      numTerms = state.getLength() - state.getNumOverlap();
+    else
+      numTerms = state.getLength();
+    return state.getBoost() * ((float) (1.0 / Math.sqrt(numTerms)));
+  }
+  
+  /** Implemented as <code>1/sqrt(sumOfSquaredWeights)</code>. */
+  @Override
+  public float queryNorm(float sumOfSquaredWeights) {
+    return (float)(1.0 / Math.sqrt(sumOfSquaredWeights));
+  }
+
+  /** Implemented as <code>sqrt(freq)</code>. */
+  @Override
+  public float tf(float freq) {
+    return (float)Math.sqrt(freq);
+  }
+    
+  /** Implemented as <code>1 / (distance + 1)</code>. */
+  @Override
+  public float sloppyFreq(int distance) {
+    return 1.0f / (distance + 1);
+  }
+    
+  /** Implemented as <code>log(numDocs/(docFreq+1)) + 1</code>. */
+  @Override
+  public float idf(int docFreq, int numDocs) {
+    return (float)(Math.log(numDocs/(double)(docFreq+1)) + 1.0);
+  }
+    
+  /** Implemented as <code>overlap / maxOverlap</code>. */
+  @Override
+  public float coord(int overlap, int maxOverlap) {
+    return overlap / (float)maxOverlap;
+  }
+
+  // Default true
+  protected boolean discountOverlaps = true;
+
+  /** Determines whether overlap tokens (Tokens with
+   *  0 position increment) are ignored when computing
+   *  norm.  By default this is true, meaning overlap
+   *  tokens do not count when computing norms.
+   *
+   *  @lucene.experimental
+   *
+   *  @see #computeNorm
+   */
+  public void setDiscountOverlaps(boolean v) {
+    discountOverlaps = v;
+  }
+
+  /** @see #setDiscountOverlaps */
+  public boolean getDiscountOverlaps() {
+    return discountOverlaps;
+  }
+}