/*
    * Licensed to the Hipparchus project under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The Hipparchus project 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.
   */
  
  package org.hipparchus.ode.nonstiff;
  
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.ode.FieldOrdinaryDifferentialEquation;
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.FieldSinCos;
  import org.hipparchus.util.MathArrays;
  
  public class Ellipse<T extends CalculusFieldElement<T>> implements FieldOrdinaryDifferentialEquation<T> {
  
      private final T a;
      private final T b;
      private final T omega;
  
      Ellipse(final T a, final T b, final T omega) {
          this.a     = a;
          this.b     = b;
          this.omega = omega;
      }
  
      @Override
      public int getDimension() {
          return 4;
      }
  
      @Override
      public T[] computeDerivatives(T t, T[] y) {
          final T[] yDot = MathArrays.buildArray(t.getField(), getDimension());
          yDot[0] = y[2];
          yDot[1] = y[3];
          yDot[2] = y[0].multiply(omega.multiply(omega).negate());
          yDot[3] = y[1].multiply(omega.multiply(omega).negate());
          return yDot;
      }
  
      public T[] computeTheoreticalState(T t) {
          final T[] y = MathArrays.buildArray(t.getField(), getDimension());
          final FieldSinCos<T> sc = FastMath.sinCos(t.multiply(omega));
          y[0] = a.multiply(sc.cos());
          y[1] = b.multiply(sc.sin());
          y[2] = a.multiply(omega).multiply(sc.sin()).negate();
          y[3] = b.multiply(omega).multiply(sc.cos());
          return y;
      }
  
  }