GoldenRatioAlgorithmStrategy.java

/*
 * Copyright (c) 2009-2015
 * 	IT-Consulting Stephan Schloepke (http://www.schloepke.de/)
 * 	klemm software consulting Mirko Klemm (http://www.klemm-scs.com/)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.jbasics.math.strategies;

import org.jbasics.math.AlgorithmStrategy;
import org.jbasics.math.IrationalNumber;
import org.jbasics.math.impl.SquareRootIrationalNumber;

import java.math.BigDecimal;
import java.math.MathContext;

public class GoldenRatioAlgorithmStrategy implements AlgorithmStrategy<BigDecimal> {
	private static final BigDecimal TWO = BigDecimal.valueOf(2l);
	private static final BigDecimal HALF = BigDecimal.ONE.divide(GoldenRatioAlgorithmStrategy.TWO);
	private static final BigDecimal FIVE = BigDecimal.valueOf(5l);
	private static final IrationalNumber<BigDecimal> SQUARE_ROOT_OF_FIVE = SquareRootIrationalNumber.valueOf(GoldenRatioAlgorithmStrategy.FIVE);

	public BigDecimal calculate(final MathContext mc, final BigDecimal guess, final BigDecimal... xn) {
		BigDecimal phi = GoldenRatioAlgorithmStrategy.HALF.add(GoldenRatioAlgorithmStrategy.SQUARE_ROOT_OF_FIVE.valueToPrecision(mc).divide(
				GoldenRatioAlgorithmStrategy.TWO), mc);
		if (xn == null || xn.length == 0) {
			return phi;
		} else {
			return phi.multiply(xn[0], mc);
		}
	}
}