/*
* Copyright (c) 2012, Søren Atmakuri Davidsen
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package fuzzy4j.sets;
import fuzzy4j.util.SimpleInterval;
/**
* Sigmoidal apply function.
*
* Defined as:
* <code>mu(x, alpha, x0) = (1 + e^(-alpha*(x-x0)))^-1</code>
*
* Where:
* x0 is the location of the x-axis position of the center of the curve.
* alpha defines the steepness of the curve. alpha is large means steep, alpha is small (<0) means less steep.
*
* @author Soren A. Davidsen <soren@tanesha.net>
*/
public class SigmoidFunction implements FuzzyFunction, SupportAware {
private double alpha;
private double x0;
public SigmoidFunction(double alpha, double x0) {
this.alpha = alpha;
this.x0 = x0;
}
@Override
public double apply(double x) {
return 1.0 / (1.0 + Math.exp(-alpha * (x - x0)));
}
@Override
public SimpleInterval support() {
double min = x0 - 9 / Math.abs(alpha);
double max = x0 + 9 / Math.abs(alpha);
return new SimpleInterval(true, min, max, true);
}
}