## Interface OrdinaryDifferentialEquation

• All Known Subinterfaces:
`FirstOrderDifferentialEquations`, `MainStateJacobianProvider`, `ODEJacobiansProvider`
All Known Implementing Classes:
`FirstOrderConverter`

`public interface OrdinaryDifferentialEquation`
This interface represents a first order differential equations set.

This interface should be implemented by all real first order differential equation problems before they can be handled by the integrators ```ODEIntegrator.integrate(OrdinaryDifferentialEquation, ODEState, double)``` method.

A first order differential equations problem, as seen by an integrator is the time derivative `dY/dt` of a state vector `Y`, both being one dimensional arrays. From the integrator point of view, this derivative depends only on the current time `t` and on the state vector `Y`.

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.

`ODEIntegrator`, `FirstOrderConverter`, `SecondOrderODE`
• ### Method Summary

All Methods
Modifier and Type Method Description
`double[]` ```computeDerivatives​(double t, double[] y)```
Get the current time derivative of the state vector.
`int` `getDimension()`
Get the dimension of the problem.
`default void` ```init​(double t0, double[] y0, double finalTime)```
Initialize equations at the start of an ODE integration.
• ### Method Detail

• #### getDimension

`int getDimension()`
Get the dimension of the problem.
Returns:
dimension of the problem
• #### init

```default void init​(double t0,
double[] y0,
double finalTime)```
Initialize equations at the start of an ODE integration.

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.

The default implementation does nothing.

Parameters:
`t0` - value of the independent time variable at integration start
`y0` - array containing the value of the state vector at integration start
`finalTime` - target time for the integration
• #### computeDerivatives

```double[] computeDerivatives​(double t,
double[] y)```
Get the current time derivative of the state vector.
Parameters:
`t` - current value of the independent time variable
`y` - array containing the current value of the state vector
Returns:
time derivative of the state vector