/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * 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
    *
    *      https://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.
   */
  
  /*
   * This is not the original file distributed by the Apache Software Foundation
   * It has been modified by the Hipparchus project
   */
  package org.hipparchus.analysis.polynomials;
  
  import org.hipparchus.exception.MathIllegalArgumentException;
  import org.junit.jupiter.api.Test;
  
  import static org.junit.jupiter.api.Assertions.assertArrayEquals;
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.fail;
  
  /**
   * Test case for Lagrange form of polynomial function.
   * <p>
   * We use n+1 points to interpolate a polynomial of degree n. This should
   * give us the exact same polynomial as result. Thus we can use a very
   * small tolerance to account only for round-off errors.
   *
   */
  final class PolynomialFunctionLagrangeFormTest {
  
      @Test
      void testGetter() {
          // GIVEN
          double[] x = { 1., 2. };
          double[] y = { -1., 4. };
          final PolynomialFunctionLagrangeForm lagrangeForm = new PolynomialFunctionLagrangeForm(x, y);
          // WHEN & THEN
          assertArrayEquals(x, lagrangeForm.getInterpolatingPoints());
          assertArrayEquals(y, lagrangeForm.getInterpolatingValues());
          assertArrayEquals(new double[] { -6., 5. }, lagrangeForm.getCoefficients());
      }
  
      @Test
      void testGetCoefficients() {
          // GIVEN
          double[] x = { 1., 2. };
          double[] y = { -1., 4. };
          final PolynomialFunctionLagrangeForm lagrangeForm = new PolynomialFunctionLagrangeForm(x, y);
          // WHEN
          final double[] coefficients = lagrangeForm.getCoefficients();
          // WHEN & THEN
          assertArrayEquals(lagrangeForm.getCoefficients(), coefficients);
      }
  
      @Test
      void testEvaluate() {
          // GIVEN
          double[] x = { 1., 2. };
          double[] y = { -1., 4. };
          final double point = 3.;
          // WHEN
          final double value = PolynomialFunctionLagrangeForm.evaluate(x, y, point);
          // THEN
          final PolynomialFunctionLagrangeForm lagrangeForm = new PolynomialFunctionLagrangeForm(x, y);
          assertEquals(lagrangeForm.value(point), value);
      }
  
      /**
       * Test of polynomial for the linear function.
       */
      @Test
      void testLinearFunction() {
          PolynomialFunctionLagrangeForm p;
          double[] c;
          double z;
          double expected;
          double result;
          double tolerance = 1E-12;
  
          // p(x) = 1.5x - 4
          double[] x = { 0.0, 3.0 };
          double[] y = { -4.0, 0.5 };
          p = new PolynomialFunctionLagrangeForm(x, y);
  
          z = 2.0; expected = -1.0; result = p.value(z);
          assertEquals(expected, result, tolerance);
  
          z = 4.5; expected = 2.75; result = p.value(z);
          assertEquals(expected, result, tolerance);
 
         z = 6.0; expected = 5.0; result = p.value(z);
         assertEquals(expected, result, tolerance);
 
         assertEquals(1, p.degree());
 
         c = p.getCoefficients();
         assertEquals(2, c.length);
         assertEquals(-4.0, c[0], tolerance);
         assertEquals(1.5, c[1], tolerance);
     }
 
     /**
      * Test of polynomial for the quadratic function.
      */
     @Test
     void testQuadraticFunction() {
         PolynomialFunctionLagrangeForm p;
         double[] c;
         double z;
         double expected;
         double result;
         double tolerance = 1E-12;
 
         // p(x) = 2x^2 + 5x - 3 = (2x - 1)(x + 3)
         double[] x = { 0.0, -1.0, 0.5 };
         double[] y = { -3.0, -6.0, 0.0 };
         p = new PolynomialFunctionLagrangeForm(x, y);
 
         z = 1.0; expected = 4.0; result = p.value(z);
         assertEquals(expected, result, tolerance);
 
         z = 2.5; expected = 22.0; result = p.value(z);
         assertEquals(expected, result, tolerance);
 
         z = -2.0; expected = -5.0; result = p.value(z);
         assertEquals(expected, result, tolerance);
 
         assertEquals(2, p.degree());
 
         c = p.getCoefficients();
         assertEquals(3, c.length);
         assertEquals(-3.0, c[0], tolerance);
         assertEquals(5.0, c[1], tolerance);
         assertEquals(2.0, c[2], tolerance);
     }
 
     /**
      * Test of polynomial for the quintic function.
      */
     @Test
     void testQuinticFunction() {
         PolynomialFunctionLagrangeForm p;
         double[] c;
         double z;
         double expected;
         double result;
         double tolerance = 1E-12;
 
         // p(x) = x^5 - x^4 - 7x^3 + x^2 + 6x = x(x^2 - 1)(x + 2)(x - 3)
         double[] x = { 1.0, -1.0, 2.0, 3.0, -3.0, 0.5 };
         double[] y = { 0.0, 0.0, -24.0, 0.0, -144.0, 2.34375 };
         p = new PolynomialFunctionLagrangeForm(x, y);
 
         z = 0.0; expected = 0.0; result = p.value(z);
         assertEquals(expected, result, tolerance);
 
         z = -2.0; expected = 0.0; result = p.value(z);
         assertEquals(expected, result, tolerance);
 
         z = 4.0; expected = 360.0; result = p.value(z);
         assertEquals(expected, result, tolerance);
 
         assertEquals(5, p.degree());
 
         c = p.getCoefficients();
         assertEquals(6, c.length);
         assertEquals(0.0, c[0], tolerance);
         assertEquals(6.0, c[1], tolerance);
         assertEquals(1.0, c[2], tolerance);
         assertEquals(-7.0, c[3], tolerance);
         assertEquals(-1.0, c[4], tolerance);
         assertEquals(1.0, c[5], tolerance);
     }
 
     /**
      * Test of parameters for the polynomial.
      */
     @Test
     void testParameters() {
 
         try {
             // bad input array length
             double[] x = { 1.0 };
             double[] y = { 2.0 };
             new PolynomialFunctionLagrangeForm(x, y);
             fail("Expecting MathIllegalArgumentException - bad input array length");
         } catch (MathIllegalArgumentException ex) {
             // expected
         }
         try {
             // mismatch input arrays
             double[] x = { 1.0, 2.0, 3.0, 4.0 };
             double[] y = { 0.0, -4.0, -24.0 };
             new PolynomialFunctionLagrangeForm(x, y);
             fail("Expecting MathIllegalArgumentException - mismatch input arrays");
         } catch (MathIllegalArgumentException ex) {
             // expected
         }
     }
 }