mathnet-numerics/src/UnitTests/DifferentiationTests/FiniteDifferenceCoefficientsTests.cs

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using MathNet.Numerics.Differentiation;
using NUnit.Framework;

namespace MathNet.Numerics.UnitTests.DifferentiationTests
{

    [TestFixture, Category("Differentiation")]
    public class FiniteDifferenceCoefficientsTests
    {
        [Test]
        public void CentralDifferenceFirstOrderThreePointTest()
        {
            double[] results = { -0.5, 0, 0.5 };
            var finite = new FiniteDifferenceCoefficients(3);
            var coeff = finite.GetCoefficients(1, 1);
            Assert.AreEqual(results, coeff);
        }

        [Test]
        public void CentralDifferenceSecondOrderFivePointsTest()
        {
            double[] results = { (double)-1 / 12, (double)4 / 3, (double)-5 / 2, (double)4 / 3, (double)-1 / 12 };
            var finite = new FiniteDifferenceCoefficients(5);
            var coeff = finite.GetCoefficients(2, 2);
            for (int i = 0; i < coeff.Length; i++)
                Assert.AreEqual(results[i], coeff[i]);
        }

        [Test]
        public void ForwardDifferenceThirdOrderEightPointsTest()
        {
            double[] results = { (double)-967 / 120, (double)638 / 15, (double)-3929 / 40, (double)389 / 3,
                                 (double)-2545 / 24, (double)268 / 5, (double)-1849 / 120, (double)29 / 15 };
            var finite = new FiniteDifferenceCoefficients(8);
            var coeff = finite.GetCoefficients(0, 3);
            for (int i = 0; i < coeff.Length; i++)
                Assert.AreEqual(results[i], coeff[i]);
        }

        [Test]
        public void BackwardDifferenceThirdOrderFourPointsTest()
        {
            double[] results = { -1, 3, -3, 1 };
            var finite = new FiniteDifferenceCoefficients(4);
            var coeff = finite.GetCoefficients(3, 3);
            for (int i = 0; i < coeff.Length; i++)
                Assert.AreEqual(results[i], coeff[i]);

        }
    }
}