/*
* 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.
*/
package org.apache.lucene.queries.function.valuesource;
import org.apache.lucene.index.AtomicReaderContext;
import org.apache.lucene.queries.function.FunctionValues;
import org.apache.lucene.queries.function.ValueSource;
import org.apache.lucene.queries.function.docvalues.FloatDocValues;
import org.apache.lucene.search.IndexSearcher;
import java.io.IOException;
import java.util.Map;
/**
* <code>ReciprocalFloatFunction</code> implements a reciprocal function f(x) = a/(mx+b), based on
* the float value of a field or function as exported by {@link org.apache.lucene.queries.function.ValueSource}.
* <br>
*
* When a and b are equal, and x>=0, this function has a maximum value of 1 that drops as x increases.
* Increasing the value of a and b together results in a movement of the entire function to a flatter part of the curve.
* <p>These properties make this an idea function for boosting more recent documents.
* <p>Example:<code> recip(ms(NOW,mydatefield),3.16e-11,1,1)</code>
* <p>A multiplier of 3.16e-11 changes the units from milliseconds to years (since there are about 3.16e10 milliseconds
* per year). Thus, a very recent date will yield a value close to 1/(0+1) or 1,
* a date a year in the past will get a multiplier of about 1/(1+1) or 1/2,
* and date two years old will yield 1/(2+1) or 1/3.
*
* @see org.apache.lucene.queries.function.FunctionQuery
*
*
*/
public class ReciprocalFloatFunction extends ValueSource {
protected final ValueSource source;
protected final float m;
protected final float a;
protected final float b;
/**
* f(source) = a/(m*float(source)+b)
*/
public ReciprocalFloatFunction(ValueSource source, float m, float a, float b) {
this.source=source;
this.m=m;
this.a=a;
this.b=b;
}
@Override
public FunctionValues getValues(Map context, AtomicReaderContext readerContext) throws IOException {
final FunctionValues vals = source.getValues(context, readerContext);
return new FloatDocValues(this) {
@Override
public float floatVal(int doc) {
return a/(m*vals.floatVal(doc) + b);
}
@Override
public String toString(int doc) {
return Float.toString(a) + "/("
+ m + "*float(" + vals.toString(doc) + ')'
+ '+' + b + ')';
}
};
}
@Override
public void createWeight(Map context, IndexSearcher searcher) throws IOException {
source.createWeight(context, searcher);
}
@Override
public String description() {
return Float.toString(a) + "/("
+ m + "*float(" + source.description() + ")"
+ "+" + b + ')';
}
@Override
public int hashCode() {
int h = Float.floatToIntBits(a) + Float.floatToIntBits(m);
h ^= (h << 13) | (h >>> 20);
return h + (Float.floatToIntBits(b)) + source.hashCode();
}
@Override
public boolean equals(Object o) {
if (ReciprocalFloatFunction.class != o.getClass()) return false;
ReciprocalFloatFunction other = (ReciprocalFloatFunction)o;
return this.m == other.m
&& this.a == other.a
&& this.b == other.b
&& this.source.equals(other.source);
}
}