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// Math.NET Numerics, part of the Math.NET Project
// http://numerics.mathdotnet.com
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using System;
using NUnit.Framework;
using MathNet.Numerics.Optimization;

namespace MathNet.Numerics.UnitTests.OptimizationTests
{
    [TestFixture]
    internal class TestBisectionRootFinder
    {
        [Test]
        public void FindRoot_Works()
        {
            var algorithm = new BisectionRootFinder(0.001, 0.001);
            var f1 = new Func<double, double>(x => (x - 3)*(x - 4));
            var r1 = algorithm.FindRoot(f1, 2.1, 3.9);
            Assert.That(Math.Abs(f1(r1)), Is.LessThan(0.001));
            Assert.That(Math.Abs(r1 - 3.0), Is.LessThan(0.001));

            var f2 = new Func<double, double>(x => (x - 3)*(x - 4));
            var r2 = algorithm.FindRoot(f1, 2.1, 3.4);
            Assert.That(Math.Abs(f2(r2)), Is.LessThan(0.001));
            Assert.That(Math.Abs(r2 - 3.0), Is.LessThan(0.001));
        }

		[Test]
		public void FindRoot_ConstantZeroRegion_HitsFirstZeroOnExpansion()
		{
			var algorithm = new BisectionRootFinder(1e-3,1e-3,lowerExpansionFactor:2,upperExpansionFactor:2);

			var r1 = algorithm.FindRoot(function_goes_flat_at_zero, -1,0);

			Assert.That(Math.Abs(r1 - 1), Is.LessThan(1e-3));

		}

		[Test]
		public void FindRoot_ConstantZeroRegion_HitsPastFirstZeroOnExpansion()
		{
			var algorithm = new BisectionRootFinder(1e-3,1e-3,lowerExpansionFactor:2,upperExpansionFactor:2);
			
			var r1 = algorithm.FindRoot(function_goes_flat_at_zero, -2.25,0);
			
			Assert.That(Math.Abs(r1 - 1), Is.LessThan(1e-3));
			
		}

		private static double function_goes_flat_at_zero(double x)
		{
			return x < 1 ? -3*(x - 1) : 0.0;
		}
    }
}