/**
 * Copyright 2010, 2011 Jingjing Li.
 *
 * This file is part of jplot2d.
 *
 * jplot2d is free software: you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or any later version.
 *
 * jplot2d is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Lesser Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with jplot2d. If not, see .
 */
package org.jplot2d.transform;

/**
 * The dest value = k * Math.log10(src value) + a.
 * 
 * @author Jingjing Li
 */
public class LogTransform implements Transform1D {

	private double k;

	private double a;

	public LogTransform() {
		super();
	}

	/**
	 * @param offset
	 *            the offset in LogarithmicNormalTransform
	 * @param scale
	 *            the scale in LogarithmicNormalTransform
	 * @param d1
	 *            the start value in destination
	 * @param d2
	 *            the end value in destination
	 */
	public LogTransform(double offset, double scale, double d1, double d2) {
		if (Double.isNaN(d1) || Double.isNaN(d2)) {
			throw new IllegalArgumentException("Transform is invalid");
		}

		k = (d2 - d1) / scale;
		a = d1 - k * offset;
	}

	public double convert(double u) {
		if (u <= 0) {
			return Double.NEGATIVE_INFINITY * k;
		}
		return k * Math.log10(u) + a;
	}

}