package org.spaceroots.mantissa.ode;

import java.io.Externalizable;

/** 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).
 *
 * @see FirstOrderIntegrator
 * @see SecondOrderIntegrator
 * @see StepHandler
 *
 * @version $Id: StepInterpolator.java 1629 2004-10-07 17:00:18Z luc $
 * @author L. Maisonobe
 *
 */

public interface StepInterpolator
  extends Externalizable {

  /**
   * Get the previous grid point time.
   * @return previous grid point time
   */
  public double getPreviousTime();
    
  /**
   * Get the current grid point time.
   * @return current grid point time
   */
  public double getCurrentTime();
    
  /**
   * Get the time of the interpolated point.
   * If {@link #setInterpolatedTime} has not been called, it returns
   * the current grid point time.
   * @return interpolation point time
   */
  public double getInterpolatedTime();
    
  /**
   * Set the time of the interpolated point.
   * 
Setting the time outside of the current step is now allowed
   * (it was not allowed up to version 5.4 of Mantissa), 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.
   * @param time time of the interpolated point
   * @throws DerivativeException if this call induces an automatic
   * step finalization that throws one
   */
  public void setInterpolatedTime(double time)
    throws DerivativeException;

  /**
   * Get the state vector of the interpolated point.
   * @return state vector at time {@link #getInterpolatedTime}
   */
  public double[] getInterpolatedState();

  /** 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 switching function
   * triggering.
   * @return true if the integration variable (time) increases during
   * integration
   */
  public boolean isForward();

}