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Scalable machine learning libraries
/*
* 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.mahout.classifier.sgd;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
/**
* Implements the Laplacian or bi-exponential prior. This prior has a strong tendency to set coefficients to zero
* and thus is useful as an alternative to variable selection. This version implements truncation which prevents
* a coefficient from changing sign. If a correction would change the sign, the coefficient is truncated to zero.
*
* Note that it doesn't matter to have a scale for this distribution because after taking the derivative of the logP,
* the lambda coefficient used to combine the prior with the observations has the same effect. If we had a scale here,
* then it would be the same effect as just changing lambda.
*/
public class L1 implements PriorFunction {
@Override
public double age(double oldValue, double generations, double learningRate) {
double newValue = oldValue - Math.signum(oldValue) * learningRate * generations;
if (newValue * oldValue < 0) {
// don't allow the value to change sign
return 0;
} else {
return newValue;
}
}
@Override
public double logP(double betaIJ) {
return -Math.abs(betaIJ);
}
@Override
public void write(DataOutput out) throws IOException {
// stateless class has nothing to serialize
}
@Override
public void readFields(DataInput dataInput) throws IOException {
// stateless class has nothing to serialize
}
}
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