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    *
    *   http://www.apache.org/licenses/LICENSE-2.0
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   * Unless required by applicable law or agreed to in writing, software
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  package org.orekit.estimation.sequential;
  
  import java.util.List;
  
  import org.orekit.propagation.PropagationType;
  import org.orekit.propagation.Propagator;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.conversion.OrbitDeterminationPropagatorBuilder;
  import org.orekit.propagation.integration.AbstractJacobiansMapper;
  import org.orekit.propagation.numerical.JacobiansMapper;
  import org.orekit.propagation.numerical.NumericalPropagator;
  import org.orekit.propagation.numerical.PartialDerivativesEquations;
  import org.orekit.utils.ParameterDriversList;
  
  /** Class defining the process model dynamics to use with a {@link KalmanEstimator}.
   * @author Romain Gerbaud
   * @author Maxime Journot
   * @since 9.2
   */
  public class KalmanModel extends AbstractKalmanModel {
  
      /** Kalman process model constructor.
       * @param propagatorBuilders propagators builders used to evaluate the orbits.
       * @param covarianceMatricesProviders providers for covariance matrices
       * @param estimatedMeasurementParameters measurement parameters to estimate
       * @param measurementProcessNoiseMatrix provider for measurement process noise matrix
       */
      public KalmanModel(final List<OrbitDeterminationPropagatorBuilder> propagatorBuilders,
                         final List<CovarianceMatrixProvider> covarianceMatricesProviders,
                         final ParameterDriversList estimatedMeasurementParameters,
                         final CovarianceMatrixProvider measurementProcessNoiseMatrix) {
          // call super constructor
          super(propagatorBuilders, covarianceMatricesProviders, estimatedMeasurementParameters,
                measurementProcessNoiseMatrix, new JacobiansMapper[propagatorBuilders.size()]);
      }
  
      /** {@inheritDoc} */
      @Override
      protected void updateReferenceTrajectories(final Propagator[] propagators,
                                                 final PropagationType pType,
                                                 final PropagationType sType) {
  
          // Update the reference trajectory propagator
          setReferenceTrajectories(propagators);
  
          // Jacobian mappers
          final AbstractJacobiansMapper[] mappers = getMappers();
  
          for (int k = 0; k < propagators.length; ++k) {
              // Link the partial derivatives to this new propagator
              final String equationName = KalmanEstimator.class.getName() + "-derivatives-" + k;
              final PartialDerivativesEquations pde = new PartialDerivativesEquations(equationName, (NumericalPropagator) getReferenceTrajectories()[k]);
  
              // Reset the Jacobians
              final SpacecraftState rawState = getReferenceTrajectories()[k].getInitialState();
              final SpacecraftState stateWithDerivatives = pde.setInitialJacobians(rawState);
              getReferenceTrajectories()[k].resetInitialState(stateWithDerivatives);
              mappers[k] = pde.getMapper();
          }
  
          // Update Jacobian mappers
          setMappers(mappers);
  
      }
  
      /** {@inheritDoc} */
      @Override
      protected void analyticalDerivativeComputations(final AbstractJacobiansMapper mapper, final SpacecraftState state) {
          // does nothing
          // numerical method does not require analytical terms calculations
      }
  
  }