view src/samer/functions/SparseExponential.java @ 0:bf79fb79ee13

Initial Mercurial check in.

/*
 *	Copyright (c) 2000, Samer Abdallah, King's College London.
 *	All rights reserved.
 *
 *	This software is provided AS iS and WITHOUT ANY WARRANTY; 
 *	without even the implied warranty of MERCHANTABILITY or 
 *	FITNESS FOR A PARTICULAR PURPOSE.
 */

package samer.functions;
import  samer.maths.*;

/**
	Single-sided (ie positive only) version of SparseLaplacian.
	See that class for a description.
  */

public class SparseExponential extends Function
{
	double beta=1, A=1;

	public void setExponent(double b) { beta=b; }
	public void setStrength(double a) { A=a; }

	public String format(String t) { return "SparseExp("+t+")"; }

	public final double apply(double t) { 
		double s=beta*t;
		if  (s<24) return t-A*Math.exp(-s);
		else return t;
	}

	public Function derivative() { 
		return new Function() {
			public String format(String t) { return "dSparseExp("+t+")"; }
			public final double apply(double t) { 
				double s=beta*t;
				if  (s>24) return 1;
				else return 1+A*beta*Math.exp(-s);
			}
		};
	}
}