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    * Licensed to the Apache Software Foundation (ASF) under one or more
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    * this work for additional information regarding copyright ownership.
    * 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
    * the License.  You may obtain a copy of the License at
    *
    *      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,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.math4.legacy.analysis.interpolation;
  
  import org.junit.Assert;
  import org.junit.Test;
  
  import org.apache.commons.rng.UniformRandomProvider;
  import org.apache.commons.rng.simple.RandomSource;
  
  import org.apache.commons.math4.legacy.analysis.UnivariateFunction;
  import org.apache.commons.math4.legacy.exception.NonMonotonicSequenceException;
  import org.apache.commons.math4.legacy.exception.NumberIsTooSmallException;
  import org.apache.commons.math4.core.jdkmath.JdkMath;
  
  
  /**
   * Test for {@link UnivariatePeriodicInterpolator}.
   */
  public class UnivariatePeriodicInterpolatorTest {
      private final UniformRandomProvider rng = RandomSource.KISS.create();
  
      @Test
      public void testSine() {
          final int n = 30;
          final double[] xval = new double[n];
          final double[] yval = new double[n];
          final double period = 12.3;
          final double offset = 45.67;
  
          double delta = 0;
          for (int i = 0; i < n; i++) {
              delta += rng.nextDouble() * period / n;
              xval[i] = offset + delta;
              yval[i] = JdkMath.sin(xval[i]);
          }
  
          final UnivariateInterpolator inter = new LinearInterpolator();
          final UnivariateFunction f = inter.interpolate(xval, yval);
  
          final UnivariateInterpolator interP
              = new UnivariatePeriodicInterpolator(new LinearInterpolator(),
                                                       period, 1);
          final UnivariateFunction fP = interP.interpolate(xval, yval);
  
          // Comparing with original interpolation algorithm.
          final double xMin = xval[0];
          final double xMax = xval[n - 1];
          for (int i = 0; i < n; i++) {
              final double x = xMin + (xMax - xMin) * rng.nextDouble();
              final double y = f.value(x);
              final double yP = fP.value(x);
  
              Assert.assertEquals("(Delta: ulp(1)) x=" + x, y, yP, Math.ulp(1d));
          }
  
          // Test interpolation outside the primary interval.
          for (int i = 0; i < n; i++) {
              final double xIn = offset + rng.nextDouble() * period;
              final double xOut = xIn + rng.nextInt(123456789) * period;
              final double yIn = fP.value(xIn);
              final double yOut = fP.value(xOut);
  
              Assert.assertEquals("Delta: 1e-7", yIn, yOut, 1e-7);
          }
      }
  
      @Test
      public void testLessThanOnePeriodCoverage() {
          final int n = 30;
          final double[] xval = new double[n];
          final double[] yval = new double[n];
          final double period = 12.3;
          final double offset = 45.67;
  
          double delta = period / 2;
          for (int i = 0; i < n; i++) {
              delta += period / (2 * n) * rng.nextDouble();
              xval[i] = offset + delta;
              yval[i] = JdkMath.sin(xval[i]);
          }
  
          final UnivariateInterpolator interP
              = new UnivariatePeriodicInterpolator(new LinearInterpolator(),
                                                       period, 1);
         final UnivariateFunction fP = interP.interpolate(xval, yval);
 
         // Test interpolation outside the sample data interval.
         for (int i = 0; i < n; i++) {
             final double xIn = offset + rng.nextDouble() * period;
             final double xOut = xIn + rng.nextInt(123456789) * period;
             final double yIn = fP.value(xIn);
             final double yOut = fP.value(xOut);
 
             Assert.assertEquals(yIn, yOut, 1e-7);
         }
     }
 
     @Test
     public void testMoreThanOnePeriodCoverage() {
         final int n = 30;
         final double[] xval = new double[n];
         final double[] yval = new double[n];
         final double period = 12.3;
         final double offset = 45.67;
 
         double delta = period / 2;
         for (int i = 0; i < n; i++) {
             delta += 10 * period / n * rng.nextDouble();
             xval[i] = offset + delta;
             yval[i] = JdkMath.sin(xval[i]);
         }
 
         final UnivariateInterpolator interP
             = new UnivariatePeriodicInterpolator(new LinearInterpolator(),
                                                      period, 1);
         final UnivariateFunction fP = interP.interpolate(xval, yval);
 
         // Test interpolation outside the sample data interval.
         for (int i = 0; i < n; i++) {
             final double xIn = offset + rng.nextDouble() * period;
             final double xOut = xIn + rng.nextInt(123456789) * period;
             final double yIn = fP.value(xIn);
             final double yOut = fP.value(xOut);
 
             Assert.assertEquals(yIn, yOut, 1e-6);
         }
     }
 
     @Test(expected=NumberIsTooSmallException.class)
     public void testTooFewSamples() {
         final double[] xval = { 2, 3, 7 };
         final double[] yval = { 1, 6, 5 };
         final double period = 10;
 
         final UnivariateInterpolator interpolator
             = new UnivariatePeriodicInterpolator(new LinearInterpolator(), period);
         interpolator.interpolate(xval, yval);
     }
 
     @Test(expected=NonMonotonicSequenceException.class)
     public void testUnsortedSamples() {
         final double[] xval = { 2, 3, 7, 4, 6 };
         final double[] yval = { 1, 6, 5, -1, -2 };
         final double period = 10;
 
         final UnivariateInterpolator interpolator
             = new UnivariatePeriodicInterpolator(new LinearInterpolator(), period);
         interpolator.interpolate(xval, yval);
     }
 }