text: ﻿// <copyright file="FiniteDifferenceCoefficientTests.cs" company="Math.NET">
  // Math.NET Numerics, part of the Math.NET Project
  // http://numerics.mathdotnet.com
  // http://github.com/mathnet/mathnet-numerics
  //
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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]);
  
          }
      }
  }
  