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    * Licensed to the Apache Software Foundation (ASF) under one or more
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    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
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    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
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   * See the License for the specific language governing permissions and
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  package org.apache.commons.math4.legacy.fitting;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Random;
  
  import org.apache.commons.numbers.angle.Angle;
  import org.apache.commons.math4.legacy.analysis.function.HarmonicOscillator;
  import org.apache.commons.math4.legacy.exception.MathIllegalStateException;
  import org.apache.commons.math4.legacy.exception.NumberIsTooSmallException;
  import org.apache.commons.math4.core.jdkmath.JdkMath;
  import org.junit.Assert;
  import org.junit.Test;
  
  public class HarmonicCurveFitterTest {
      /**
       * Zero points is not enough observed points.
       */
      @Test(expected=NumberIsTooSmallException.class)
      public void testPreconditions1() {
          HarmonicCurveFitter.create().fit(new WeightedObservedPoints().toList());
      }
  
      @Test
      public void testNoError() {
          final double a = 0.2;
          final double w = 3.4;
          final double p = 4.1;
          final HarmonicOscillator f = new HarmonicOscillator(a, w, p);
  
          final WeightedObservedPoints points = new WeightedObservedPoints();
          for (double x = 0.0; x < 1.3; x += 0.01) {
              points.add(1, x, f.value(x));
          }
  
          final SimpleCurveFitter fitter = HarmonicCurveFitter.create();
          final double[] fitted = fitter.fit(points.toList());
          Assert.assertEquals(a, fitted[0], 1.0e-13);
          Assert.assertEquals(w, fitted[1], 1.0e-13);
          Assert.assertEquals(p, Angle.Rad.WITHIN_0_AND_2PI.applyAsDouble(fitted[2]), 1e-13);
  
          final HarmonicOscillator ff = new HarmonicOscillator(fitted[0], fitted[1], fitted[2]);
          for (double x = -1.0; x < 1.0; x += 0.01) {
              Assert.assertTrue(JdkMath.abs(f.value(x) - ff.value(x)) < 1e-13);
          }
      }
  
      @Test
      public void test1PercentError() {
          final Random randomizer = new Random(64925784252L);
          final double a = 0.2;
          final double w = 3.4;
          final double p = 4.1;
          final HarmonicOscillator f = new HarmonicOscillator(a, w, p);
  
          final WeightedObservedPoints points = new WeightedObservedPoints();
          for (double x = 0.0; x < 10.0; x += 0.1) {
              points.add(1, x, f.value(x) + 0.01 * randomizer.nextGaussian());
          }
  
          final SimpleCurveFitter fitter = HarmonicCurveFitter.create();
          final double[] fitted = fitter.fit(points.toList());
          Assert.assertEquals(a, fitted[0], 7.6e-4);
          Assert.assertEquals(w, fitted[1], 2.7e-3);
          Assert.assertEquals(p, Angle.Rad.WITHIN_0_AND_2PI.applyAsDouble(fitted[2]), 1.3e-2);
      }
  
      @Test
      public void testTinyVariationsData() {
          final Random randomizer = new Random(64925784252L);
  
          final WeightedObservedPoints points = new WeightedObservedPoints();
          for (double x = 0.0; x < 10.0; x += 0.1) {
              points.add(1, x, 1e-7 * randomizer.nextGaussian());
          }
  
          final SimpleCurveFitter fitter = HarmonicCurveFitter.create();
          fitter.fit(points.toList());
  
          // This test serves to cover the part of the code of "guessAOmega"
          // when the algorithm using integrals fails.
      }
  
     @Test
     public void testInitialGuess() {
         final Random randomizer = new Random(45314242L);
         final double a = 0.2;
         final double w = 3.4;
         final double p = 4.1;
         final HarmonicOscillator f = new HarmonicOscillator(a, w, p);
 
         final WeightedObservedPoints points = new WeightedObservedPoints();
         for (double x = 0.0; x < 10.0; x += 0.1) {
             points.add(1, x, f.value(x) + 0.01 * randomizer.nextGaussian());
         }
 
         final SimpleCurveFitter fitter = HarmonicCurveFitter.create()
             .withStartPoint(new double[] { 0.15, 3.6, 4.5 });
         final double[] fitted = fitter.fit(points.toList());
         Assert.assertEquals(a, fitted[0], 1.2e-3);
         Assert.assertEquals(w, fitted[1], 3.3e-3);
         Assert.assertEquals(p, Angle.Rad.WITHIN_0_AND_2PI.applyAsDouble(fitted[2]), 1.7e-2);
     }
 
     @Test
     public void testUnsorted() {
         Random randomizer = new Random(64925784252L);
         final double a = 0.2;
         final double w = 3.4;
         final double p = 4.1;
         final HarmonicOscillator f = new HarmonicOscillator(a, w, p);
 
         // Build a regularly spaced array of measurements.
         final int size = 100;
         final double[] xTab = new double[size];
         final double[] yTab = new double[size];
         for (int i = 0; i < size; i++) {
             xTab[i] = 0.1 * i;
             yTab[i] = f.value(xTab[i]) + 0.01 * randomizer.nextGaussian();
         }
 
         // shake it
         for (int i = 0; i < size; i++) {
             int i1 = randomizer.nextInt(size);
             int i2 = randomizer.nextInt(size);
             double xTmp = xTab[i1];
             double yTmp = yTab[i1];
             xTab[i1] = xTab[i2];
             yTab[i1] = yTab[i2];
             xTab[i2] = xTmp;
             yTab[i2] = yTmp;
         }
 
         // Pass it to the fitter.
         final WeightedObservedPoints points = new WeightedObservedPoints();
         for (int i = 0; i < size; ++i) {
             points.add(1, xTab[i], yTab[i]);
         }
 
         final SimpleCurveFitter fitter = HarmonicCurveFitter.create();
         final double[] fitted = fitter.fit(points.toList());
         Assert.assertEquals(a, fitted[0], 7.6e-4);
         Assert.assertEquals(w, fitted[1], 3.5e-3);
         Assert.assertEquals(p, Angle.Rad.WITHIN_0_AND_2PI.applyAsDouble(fitted[2]), 1.5e-2);
     }
 
     @Test(expected=MathIllegalStateException.class)
     public void testMath844() {
         final double[] y = { 0, 1, 2, 3, 2, 1,
                              0, -1, -2, -3, -2, -1,
                              0, 1, 2, 3, 2, 1,
                              0, -1, -2, -3, -2, -1,
                              0, 1, 2, 3, 2, 1, 0 };
         final List<WeightedObservedPoint> points = new ArrayList<>();
         for (int i = 0; i < y.length; i++) {
             points.add(new WeightedObservedPoint(1, i, y[i]));
         }
 
         // The guesser fails because the function is far from an harmonic
         // function: It is a triangular periodic function with amplitude 3
         // and period 12, and all sample points are taken at integer abscissae
         // so function values all belong to the integer subset {-3, -2, -1, 0,
         // 1, 2, 3}.
         new HarmonicCurveFitter.ParameterGuesser().guess(points);
     }
 }