org.apache.commons.math3.ode.sampling

## Interface FieldStepInterpolator<T extends RealFieldElement<T>>

- Type Parameters:
    `T` - the type of the field elements
  All Known Implementing Classes:
    AbstractFieldStepInterpolator

      public interface FieldStepInterpolator<T extends RealFieldElement<T>>

  This interface represents an interpolator over the last step during an ODE integration.

  The various ODE integrators provide objects implementing this interface to the step handlers. These objects are often custom objects tightly bound to the integrator internal algorithms. The handlers can use these objects to retrieve the state vector at intermediate times between the previous and the current grid points (this feature is often called dense output).

  Since:
    3.6
  See Also:
    `FirstOrderFieldIntegrator`, `FieldStepHandler`

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `FieldODEStateAndDerivative<T>` | `getCurrentState()` Get the state at current grid point time.
    `FieldODEStateAndDerivative<T>` | `getInterpolatedState(T time)` Get the state at interpolated time.
    `FieldODEStateAndDerivative<T>` | `getPreviousState()` Get the state at previous grid point time.
    `boolean` | `isForward()` Check if the natural integration direction is forward.

- - ### Method Detail

    - #### getPreviousState

          FieldODEStateAndDerivative<T> getPreviousState()

      Get the state at previous grid point time.
      Returns:
        state at previous grid point time

    - #### getCurrentState

          FieldODEStateAndDerivative<T> getCurrentState()

      Get the state at current grid point time.
      Returns:
        state at current grid point time

    - #### getInterpolatedState

          FieldODEStateAndDerivative<T> getInterpolatedState(T time)

      Get the state at interpolated time.

      Setting the time outside of the current step is allowed, but should be used with care since the accuracy of the interpolator will probably be very poor far from this step. This allowance has been added to simplify implementation of search algorithms near the step endpoints.

      Parameters:
        `time` - time of the interpolated point
      Returns:
        state at interpolated time

    - #### isForward

          boolean isForward()

      Check if the natural integration direction is forward.

      This method provides the integration direction as specified by the integrator itself, it avoid some nasty problems in degenerated cases like null steps due to cancellation at step initialization, step control or discrete events triggering.

      Returns:
        true if the integration variable (time) increases during integration

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