```
/*
* 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.ode;
import org.hipparchus.CalculusFieldElement;
/** This interface represents a first order differential equations set.
*
* <p>This interface should be implemented by all real first order
* differential equation problems before they can be handled by the
* integrators {@link FieldODEIntegrator#integrate(FieldExpandableODE,
* FieldODEState, CalculusFieldElement)} method.</p>
*
* <p>A first order differential equations problem, as seen by an
* integrator is the time derivative <code>dY/dt</code> of a state
* vector <code>Y</code>, both being one dimensional arrays. From the
* integrator point of view, this derivative depends only on the
* current time <code>t</code> and on the state vector
* <code>Y</code>.</p>
*
* <p>For real problems, the derivative depends also on parameters
* that do not belong to the state vector (dynamical model constants
* for example). These constants are completely outside of the scope
* of this interface, the classes that implement it are allowed to
* handle them as they want.</p>
*
* @see FieldODEIntegrator
*
* @param <T> the type of the field elements
*/
public interface FieldOrdinaryDifferentialEquation<T extends CalculusFieldElement<T>> {
/** Get the dimension of the problem.
* @return dimension of the problem
*/
int getDimension();
/** Initialize equations at the start of an ODE integration.
* <p>
* This method is called once at the start of the integration. It
* may be used by the equations to initialize some internal data
* if needed.
* </p>
* <p>
* The default implementation does nothing.
* </p>
* @param t0 value of the independent <I>time</I> variable at integration start
* @param y0 array containing the value of the state vector at integration start
* @param finalTime target time for the integration
*/
default void init(T t0, T[] y0, T finalTime) {
// do nothing by default
}
/** Get the current time derivative of the state vector.
* @param t current value of the independent <I>time</I> variable
* @param y array containing the current value of the state vector
* @return time derivative of the state vector
*/
T[] computeDerivatives(T t, T[] y);
}
```