Approximates the atan function. - Java java.lang

Java examples for java.lang:Math Trigonometric Function

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Description

Approximates the atan function.

Demo Code

/*//from   ww w .  java  2s  .c o  m
 * Created on 02-May-2006 at 17:31:01.
 * 
 * Copyright (c) 2010 Robert Virkus / Enough Software
 *
 * This file is part of J2ME Polish.
 *
 * J2ME Polish is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * J2ME Polish 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 Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with J2ME Polish; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * 
 * Commercial licenses are also available, please
 * refer to the accompanying LICENSE.txt or visit
 * http://www.j2mepolish.org for details.
 */
//package com.java2s;

public class Main {
    /**
     * Approximates the atan function. Uses a polynomial approximation that should
     * be accurate enough for most practical purposes.
     * 
     * @param x
     * @return the calculated value
     */
    public static double atan(double x) {
        double SQRT3 = 1.732050807568877294;
        boolean signChange = false;
        boolean Invert = false;
        int sp = 0;
        double x2, a;
        // check up the sign change
        if (x < 0.) {
            x = -x;
            signChange = true;
        }
        // check up the invertation
        if (x > 1.) {
            x = 1 / x;
            Invert = true;
        }
        // process shrinking the domain until x<PI/12
        while (x > Math.PI / 12) {
            sp++;
            a = x + SQRT3;
            a = 1 / a;
            x = x * SQRT3;
            x = x - 1;
            x = x * a;
        }
        // calculation core
        x2 = x * x;
        a = x2 + 1.4087812;
        a = 0.55913709 / a;
        a = a + 0.60310579;
        a = a - (x2 * 0.05160454);
        a = a * x;
        // process until sp=0
        while (sp > 0) {
            a = a + Math.PI / 6;
            sp--;
        }
        // inversation took place
        if (Invert)
            a = Math.PI / 2 - a;
        // sign change took place
        if (signChange)
            a = -a;
        //
        return a;
    }
}

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