001/** 
002 * Copyright (c) 2009, Regents of the University of Colorado 
003 * All rights reserved.
004 * 
005 * Redistribution and use in source and binary forms, with or without
006 * modification, are permitted provided that the following conditions are met:
007 * 
008 * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 
009 * 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. 
010 * Neither the name of the University of Colorado at Boulder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. 
011 * 
012 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
013 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
014 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
015 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
016 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
017 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
018 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
019 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
020 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
021 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
022 * POSSIBILITY OF SUCH DAMAGE. 
023 */
024
025package org.cleartk.ml.sigmoid;
026
027import java.io.Serializable;
028
029/**
030 * <br>
031 * Copyright (c) 2009, Regents of the University of Colorado <br>
032 * All rights reserved.
033 * <p>
034 */
035public class Sigmoid implements Serializable {
036
037  private static final long serialVersionUID = 3780856549630884460L;
038
039  public Sigmoid(double A, double B) {
040    this.A = A;
041    this.B = B;
042  }
043
044  public double evaluate(double v) {
045    return 1 / (1 + Math.exp(A * v + B));
046  }
047
048  public double getA() {
049    return A;
050  }
051
052  public double getB() {
053    return B;
054  }
055
056  @Override
057  public String toString() {
058    if (B < 0)
059      return String.format("1 / (1 + exp(%.3f*x - %.3f))", A, -B);
060    else
061      return String.format("1 / (1 + exp(%.3f*x + %.3f))", A, B);
062  }
063
064  private double A;
065
066  private double B;
067}