/*
    * 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.function;
  
  import org.hipparchus.analysis.UnivariateFunction;
  import org.hipparchus.analysis.differentiation.DSFactory;
  import org.hipparchus.analysis.differentiation.DerivativeStructure;
  import org.hipparchus.analysis.differentiation.UnivariateDifferentiableFunction;
  import org.hipparchus.util.FastMath;
  import org.junit.jupiter.api.Test;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  
  class SqrtTest {
      @Test
      void testComparison() {
         final Sqrt s = new Sqrt();
         final UnivariateFunction f = new UnivariateFunction() {
             @Override
             public double value(double x) {
                 return FastMath.sqrt(x);
             }
         };
  
         for (double x = 1e-30; x < 1e10; x *= 2) {
             final double fX = f.value(x);
             final double sX = s.value(x);
             assertEquals(fX, sX, 0, "x=" + x);
         }
     }
  
      @Test
      void testDerivativeComparison() {
         final UnivariateDifferentiableFunction sPrime = new Sqrt();
         final UnivariateFunction f = new UnivariateFunction() {
                 @Override
              public double value(double x) {
                     return 1 / (2 * FastMath.sqrt(x));
                 }
             };
  
         DSFactory factory = new DSFactory(1, 1);
         for (double x = 1e-30; x < 1e10; x *= 2) {
             final double fX = f.value(x);
             final double sX = sPrime.value(factory.variable(0, x)).getPartialDerivative(1);
             assertEquals(fX, sX, FastMath.ulp(fX), "x=" + x);
         }
     }
  
      @Test
      void testDerivativesHighOrder() {
         DerivativeStructure s = new Sqrt().value(new DSFactory(1, 5).variable(0, 1.2));
         assertEquals(1.0954451150103322269, s.getPartialDerivative(0), 1.0e-16);
         assertEquals(0.45643546458763842789, s.getPartialDerivative(1), 1.0e-16);
         assertEquals(-0.1901814435781826783,  s.getPartialDerivative(2), 1.0e-16);
         assertEquals(0.23772680447272834785,  s.getPartialDerivative(3), 1.0e-16);
         assertEquals(-0.49526417598485072465,   s.getPartialDerivative(4), 5.0e-16);
         assertEquals(1.4445205132891479465,  s.getPartialDerivative(5), 7.0e-16);
     }
  
  }