fuzzy.mf.DifferentialSigmoidalMembershipFunction.java Source code

Introduction

Here is the source code for fuzzy.mf.DifferentialSigmoidalMembershipFunction.java

Source

/*
 * 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 fuzzy.mf;

import org.apache.commons.math3.analysis.function.Sigmoid;

/**
 * Differential Sigmoidal Membership Function. Equivalent to Matlab 
 * <a href="http://www.mathworks.com/help/toolbox/fuzzy/dsigmf.html">dsigmf</a> 
 * function. 
 *
 * @since 0.1
 */
public class DifferentialSigmoidalMembershipFunction implements MembershipFunction<Double> {

    protected final static double DEFAULT_LOW_ASYMPTOTE = 0.0;
    protected final static double DEFAULT_HIGH_ASYMPTOTE = 1.0;

    protected transient Sigmoid sigmoid;

    private final double a1;
    private final double c1;
    private final double a2;
    private final double c2;

    public DifferentialSigmoidalMembershipFunction(double a1, double c1, double a2, double c2) {
        this(DEFAULT_LOW_ASYMPTOTE, DEFAULT_HIGH_ASYMPTOTE, a1, c1, a2, c2);
    }

    public DifferentialSigmoidalMembershipFunction(double lowAsymptote, double highAsymptote, double a1, double c1,
            double a2, double c2) {
        sigmoid = new Sigmoid(lowAsymptote, highAsymptote);
        this.a1 = a1;
        this.c1 = c1;
        this.a2 = a2;
        this.c2 = c2;
    }

    public Double evaluate(Double x) {
        final double r1 = sigmoid.value(a1 * (x - c1));
        final double r2 = sigmoid.value(a2 * (x - c2));

        return r1 - r2;
    }

    /* (non-Javadoc)
     * @see java.lang.Object#equals(java.lang.Object)
     */
    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof DifferentialSigmoidalMembershipFunction)) {
            return false;
        }
        final DifferentialSigmoidalMembershipFunction that = (DifferentialSigmoidalMembershipFunction) obj;
        return this.a1 == that.a1 && this.c1 == that.c1 && this.a2 == that.a2 && this.c2 == that.c2;
    }

    /* (non-Javadoc)
     * @see java.lang.Object#hashCode()
     */
    @Override
    public int hashCode() {
        int hash = "DifferentialSigmoidalMembershipFunction".hashCode();
        hash <<= 2;
        hash ^= (int) this.a1;
        hash <<= 2;
        hash ^= (int) this.c1;
        hash <<= 2;
        hash ^= (int) this.a2;
        hash <<= 2;
        hash ^= (int) this.c2;
        return hash;
    }

    /* (non-Javadoc)
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        return "Differential Sigmoidal Membership Function [" + a1 + " " + c1 + " " + a2 + " " + c2 + "]";
    }

}