/* Copyright 2002-2025 CS GROUP
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS 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,
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  package org.orekit.utils;
  
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.Precision;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.Test;
  import org.orekit.time.AbsoluteDate;
  
  public class DifferentiationTest {
  
      @Test
      public void testScaleOne() {
          // with this step, computation is exact in IEEE754
          doTestScale(1.0, FastMath.pow(1.0, -3), Precision.SAFE_MIN);
      }
  
      @Test
      public void testScalePowerOfTwoStepRepresentableNumber() {
          // with this step, computation is exact in IEEE754
          doTestScale(FastMath.scalb(1.0, -10), FastMath.pow(1.0, -7), Precision.SAFE_MIN);
      }
  
      @Test
      public void testScalePowerOfTwoStepNonRepresentableNumber() {
          // with this step, computation has numerical noise
          doTestScale(FastMath.scalb(1.0, -10), 0.007, 1.7e-12);
      }
  
      private void doTestScale(final double scale, final double step, final double tolerance) {
          ParameterDriver   driver = new ParameterDriver("", -100.0, scale,
                                                         Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
          ParameterFunction f0     = (d,t) -> 3 * d.getValue(t) * d.getValue(t) - 2 * d.getValue(t);
          ParameterFunction f1Diff = Differentiation.differentiate(f0, 4, step);
          ParameterFunction f1Ref  = (d,t) -> 6 * d.getValue(t) - 2;
  
          for (double x = -3.0; x < 3.0; x += 0.125) {
              driver.setValue(x);
              Assertions.assertEquals(f1Ref.value(driver, new AbsoluteDate()), f1Diff.value(driver, new AbsoluteDate()), tolerance);
          }
  
      }
  
  }