/*
 * [TestATan2.java]
 *
 * Summary: Explore how Math.atan2 works.
 *
 * Copyright: (c) 2011-2017 Roedy Green, Canadian Mind Products, http://mindprod.com
 *
 * Licence: This software may be copied and used freely for any purpose but military.
 *          http://mindprod.com/contact/nonmil.html
 *
 * Requires: JDK 1.8+
 *
 * Created with: JetBrains IntelliJ IDEA IDE http://www.jetbrains.com/idea/
 *
 * Version History:
 *  1.0 2011-01-14 initial version
 */
package com.mindprod.test;

import java.text.DecimalFormat;

import static java.lang.System.*;

/**
 * Explore how Math.atan2 works.
 * <p/>
 * s.
 *
 * @author Roedy Green, Canadian Mind Products
 * @version 1.0 2011-01-14 initial version
 * @since 2011-01-14
 */
public final class TestATan2
    {
    private static final DecimalFormat df = new DecimalFormat( "#0.000" );

    /**
     * diplay facts about one multiple of pi/4
     *
     * @param multiple multiple of pi/4
     * @param y        y to take atan2 of
     * @param x        y to take atan2 of
     */
    private static void show( int multiple, int y, int x )
        {
        double a = Math.atan2( y, x );
        out.println( Math.toDegrees( Math.PI * multiple / 4 )
                     + " "
                     + df.format( Math.tan( Math.PI * multiple / 4 ) )
                     + " "
                     + df.format( a )
                     + " "
                     + df.format( Math.toDegrees( a ) ) );
        }

    /**
     * main program to test average-calculating code.
     *
     * @param args command line not used.
     */
    public static void main( String[] args )
        {
        // the result of Math.atan2 is always in the range -pi to + pi in radians.   (-180 to 180 degrees).
        // Several different numbers map to the same tangent.  atan2 cleverly selects the one that is in the quadrant
        // of y then x.
        // Note the order y, x since tan is y/x.
        // Note how Math.toDegrees normalise the output to -180 .. +180 degrees.
        // bottom right quadrant
        show( 7, 1, -1 );
        // bottom left quadrant
        show( 5, -1, -1 );
        // top left quadrant
        show( 3, -1, 1 );
        // y axis
        show( 2, 0, 1 );
        // top right quadrant
        show( 1, 1, 1 );
        // x axis
        show( 0, 1, 0 );
        // bottom right quadrant
        show( -1, 1, -1 );
        // bottom left quadrant
        show( -3, -1, -1 );
        // top left quadrant
        show( -5, -1, 1 );
        // top right quadrant
        show( -7, 1, 1 );
        // prints
        // 315.0 -1.000 2.356 135.000
        // 225.0 1.000 -2.356 -135.000
        // 135.0 -1.000 -0.785 -45.000
        // 90.0 16331239353195370.000 0.000 0.000
        // 45.0 1.000 0.785 45.000
        // 0.0 0.000 1.571 90.000
        // -45.0 -1.000 2.356 135.000
        // -135.0 1.000 -2.356 -135.000
        // -225.0 -1.000 -0.785 -45.000
        // -315.0 1.000 0.785 45.000
        }
    }