it.uniroma2.sag.kelp.kernel.standard.NormalizationKernel.java Source code

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Here is the source code for it.uniroma2.sag.kelp.kernel.standard.NormalizationKernel.java

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/*
 * Copyright 2014 Simone Filice and Giuseppe Castellucci and Danilo Croce and Roberto Basili
 * Licensed 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 it.uniroma2.sag.kelp.kernel.standard;

import it.uniroma2.sag.kelp.data.example.Example;
import it.uniroma2.sag.kelp.kernel.Kernel;
import it.uniroma2.sag.kelp.kernel.KernelComposition;

import com.fasterxml.jackson.annotation.JsonTypeName;

/**
 * Normalization of a generic kernel K</br>
 * 
 * Normalization formula: \(K(x,y) = \frac{K(x,y)}{\sqrt{(K(x,x) \cdot K(y,y))}}\)
 * 
 * @author Simone Filice
 */
@JsonTypeName("norm")
public class NormalizationKernel extends KernelComposition {

    public NormalizationKernel(Kernel kernelToNormalize) {
        this.baseKernel = kernelToNormalize;
    }

    public NormalizationKernel() {

    }

    @Override
    protected float kernelComputation(Example exA, Example exB) {
        Float qNormA = this.baseKernel.squaredNorm(exA);
        if (qNormA == 0) {
            return 0;
        }
        Float qNormB = this.baseKernel.squaredNorm(exB);
        if (qNormB == 0) {
            return 0;
        }
        float kernelVal = this.baseKernel.innerProduct(exA, exB);

        return (float) (kernelVal / (Math.sqrt(qNormA * qNormB)));
    }

    @Override
    public float squaredNorm(Example example) {
        return 1;
    }
}