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    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS 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
    *
    *   http://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,
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  package org.orekit.propagation.numerical;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.List;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.hipparchus.ode.FieldODEIntegrator;
  import org.hipparchus.util.MathArrays;
  import org.orekit.annotation.DefaultDataContext;
  import org.orekit.attitudes.AttitudeProvider;
  import org.orekit.attitudes.FieldAttitude;
  import org.orekit.data.DataContext;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitIllegalArgumentException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.forces.ForceModel;
  import org.orekit.forces.gravity.NewtonianAttraction;
  import org.orekit.frames.Frame;
  import org.orekit.orbits.FieldOrbit;
  import org.orekit.orbits.OrbitParamsType;
  import org.orekit.orbits.PositionAngleType;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.PropagationType;
  import org.orekit.propagation.Propagator;
  import org.orekit.propagation.events.FieldEventDetector;
  import org.orekit.propagation.integration.FieldAbstractIntegratedPropagator;
  import org.orekit.propagation.integration.FieldStateMapper;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.utils.FieldAbsolutePVCoordinates;
  import org.orekit.utils.TimeStampedFieldPVCoordinates;
  
  /** This class propagates {@link org.orekit.orbits.FieldOrbit orbits} using
   * numerical integration.
   * <p>Numerical propagation is much more accurate than analytical propagation
   * like for example {@link org.orekit.propagation.analytical.KeplerianPropagator
   * Keplerian} or {@link org.orekit.propagation.analytical.EcksteinHechlerPropagator
   * Eckstein-Hechler}, but requires a few more steps to set up to be used properly.
   * Whereas analytical propagators are configured only thanks to their various
   * constructors and can be used immediately after construction, numerical propagators
   * configuration involve setting several parameters between construction time
   * and propagation time.</p>
   * <p>The configuration parameters that can be set are:</p>
   * <ul>
   *   <li>the initial spacecraft state ({@link #setInitialState(FieldSpacecraftState)})</li>
   *   <li>the central attraction coefficient ({@link #setMu(CalculusFieldElement)})</li>
   *   <li>the various force models ({@link #addForceModel(ForceModel)},
   *   {@link #removeForceModels()})</li>
   *   <li>the {@link OrbitParamsType type} of orbital parameters to be used for propagation
   *   ({@link #setOrbitParamsType(OrbitParamsType)}),
   *   <li>the {@link PositionAngleType type} of position angle to be used in orbital parameters
   *   to be used for propagation where it is relevant ({@link
   *   #setPositionAngleType(PositionAngleType)}),
   *   <li>whether {@link org.orekit.propagation.integration.FieldAdditionalDerivativesProvider additional derivatives providers}
   *   should be propagated along with orbital state
   *   ({@link #addAdditionalDerivativesProvider(org.orekit.propagation.integration.FieldAdditionalDerivativesProvider)}),
   *   <li>the discrete events that should be triggered during propagation
   *   ({@link #addEventDetector(FieldEventDetector)},
   *   {@link #clearEventsDetectors()})</li>
   *   <li>the binding logic with the rest of the application ({@link #getMultiplexer()})</li>
   * </ul>
   * <p>From these configuration parameters, only the initial state is mandatory. The default
   * propagation settings are in {@link OrbitParamsType#EQUINOCTIAL equinoctial} parameters with
   * {@link PositionAngleType#ECCENTRIC} longitude argument. If the central attraction coefficient
   * is not explicitly specified, the one used to define the initial orbit will be used.
   * However, specifying only the initial state and perhaps the central attraction coefficient
   * would mean the propagator would use only Keplerian forces. In this case, the simpler {@link
   * org.orekit.propagation.analytical.KeplerianPropagator KeplerianPropagator} class would
   * perhaps be more effective.</p>
   * <p>The underlying numerical integrator set up in the constructor may also have its own
   * configuration parameters. Typical configuration parameters for adaptive stepsize integrators
   * are the min, max and perhaps start step size as well as the absolute and/or relative errors
   * thresholds.</p>
   * <p>The state that is seen by the integrator is a simple seven elements double array.
   * The six first elements are either:
   * <ul>
   *   <li>the {@link org.orekit.orbits.FieldEquinoctialOrbit equinoctial orbit parameters} (a, e<sub>x</sub>,
   *   e<sub>y</sub>, h<sub>x</sub>, h<sub>y</sub>, λ<sub>M</sub> or λ<sub>E</sub>
   *   or λ<sub>v</sub>) in meters and radians,</li>
   *   <li>the {@link org.orekit.orbits.FieldKeplerianOrbit Keplerian orbit parameters} (a, e, i, ω, Ω,
   *   M or E or v) in meters and radians,</li>
  *   <li>the {@link org.orekit.orbits.FieldCircularOrbit circular orbit parameters} (a, e<sub>x</sub>, e<sub>y</sub>, i,
  *   Ω, α<sub>M</sub> or α<sub>E</sub> or α<sub>v</sub>) in meters
  *   and radians,</li>
  *   <li>the {@link org.orekit.orbits.FieldCartesianOrbit Cartesian orbit parameters} (x, y, z, v<sub>x</sub>,
  *   v<sub>y</sub>, v<sub>z</sub>) in meters and meters per seconds.
  * </ul>
  * The last element is the mass in kilograms.
  * <p>The following code snippet shows a typical setting for Low Earth Orbit propagation in
  * equinoctial parameters and true longitude argument:</p>
  * <pre>
  * final T          zero      = field.getZero();
  * final T          dP        = zero.add(0.001);
  * final T          minStep   = zero.add(0.001);
  * final T          maxStep   = zero.add(500);
  * final T          initStep  = zero.add(60);
  * final double[][] tolerance = ToleranceProvider.getDefaultToleranceProvider(dP).getTolerances(orbit, OrbitType.EQUINOCTIAL);
  * AdaptiveStepsizeFieldIntegrator&lt;T&gt; integrator = new DormandPrince853FieldIntegrator&lt;&gt;(field, minStep, maxStep, tolerance[0], tolerance[1]);
  * integrator.setInitialStepSize(initStep);
  * propagator = new FieldNumericalPropagator&lt;&gt;(field, integrator);
  * </pre>
  * <p>By default, at the end of the propagation, the propagator resets the initial state to the final state,
  * thus allowing a new propagation to be started from there without recomputing the part already performed.
  * This behaviour can be changed by calling {@link #setResetAtEnd(boolean)}.
  * </p>
  * <p>Beware the same instance cannot be used simultaneously by different threads, the class is <em>not</em>
  * thread-safe.</p>
 
  * @see FieldSpacecraftState
  * @see ForceModel
  * @see org.orekit.propagation.sampling.FieldOrekitStepHandler
  * @see org.orekit.propagation.sampling.FieldOrekitFixedStepHandler
  * @see org.orekit.propagation.integration.FieldIntegratedEphemeris
  * @see FieldTimeDerivativesEquations
  *
  * @author Mathieu Rom&eacute;ro
  * @author Luc Maisonobe
  * @author Guylaine Prat
  * @author Fabien Maussion
  * @author V&eacute;ronique Pommier-Maurussane
  * @param <T> type of the field elements
  */
 public class FieldNumericalPropagator<T extends CalculusFieldElement<T>> extends FieldAbstractIntegratedPropagator<T> {
 
     /** Force models used during the extrapolation of the orbit, without Jacobians. */
     private final List<ForceModel> forceModels;
 
     /** boolean to ignore or not the creation of a NewtonianAttraction. */
     private boolean ignoreCentralAttraction = false;
 
     /**
      * boolean to know if a full attitude (with rates) is needed when computing derivatives for the ODE.
      */
     private boolean needFullAttitudeForDerivatives = true;
 
     /**
      * Create a new instance of NumericalPropagator, based on orbit definition mu.
      * After creation, the instance is empty, i.e. the attitude provider is set to an
      * unspecified default law and there are no perturbing forces at all.
      * This means that if {@link #addForceModel addForceModel} is not
      * called after creation, the integrated orbit will follow a Keplerian
      * evolution only. The defaults are {@link OrbitParamsType#EQUINOCTIAL}
      * for {@link #setOrbitParamsType(OrbitParamsType) propagation
      * orbit type} and {@link PositionAngleType#ECCENTRIC} for {@link
      * #setPositionAngleType(PositionAngleType) position angle type}.
      *
      * <p>This constructor uses the {@link DataContext#getDefault() default data context}.
      *
      * @param integrator numerical integrator to use for propagation.
      * @see #FieldNumericalPropagator(FieldODEIntegrator, AttitudeProvider)
      */
     @DefaultDataContext
     public FieldNumericalPropagator(final FieldODEIntegrator<T> integrator) {
         this(integrator, Propagator.getDefaultLaw(DataContext.getDefault().getFrames()));
     }
 
     /**
      * Create a new instance of NumericalPropagator, based on orbit definition mu.
      * After creation, the instance is empty, i.e. the attitude provider is set to an
      * unspecified default law and there are no perturbing forces at all.
      * This means that if {@link #addForceModel addForceModel} is not
      * called after creation, the integrated orbit will follow a Keplerian
      * evolution only. The defaults are {@link OrbitParamsType#EQUINOCTIAL}
      * for {@link #setOrbitParamsType(OrbitParamsType) propagation
      * orbit type} and {@link PositionAngleType#ECCENTRIC} for {@link
      * #setPositionAngleType(PositionAngleType) position angle type}.
      *
      * @param integrator       numerical integrator to use for propagation.
      * @param attitudeProvider attitude law to use.
      * @since 10.1
      */
     public FieldNumericalPropagator(final FieldODEIntegrator<T> integrator,
                                     final AttitudeProvider attitudeProvider) {
         super(integrator.getCurrentSignedStepsize().getField(), integrator, PropagationType.OSCULATING);
         forceModels = new ArrayList<>();
         initMapper(getField());
         setAttitudeProvider(attitudeProvider);
         setMu(getField().getZero().add(Double.NaN));
         clearStepHandlers();
         setOrbitParamsType(NumericalPropagator.DEFAULT_ORBIT_TYPE);
         setPositionAngleType(NumericalPropagator.DEFAULT_POSITION_ANGLE_TYPE);
     }
 
     /** Set the flag to ignore or not the creation of a {@link NewtonianAttraction}.
      * @param ignoreCentralAttraction if true, {@link NewtonianAttraction} is <em>not</em>
      * added automatically if missing
      */
     public void setIgnoreCentralAttraction(final boolean ignoreCentralAttraction) {
         this.ignoreCentralAttraction = ignoreCentralAttraction;
     }
 
     /** Set the central attraction coefficient μ.
      * <p>
      * Setting the central attraction coefficient is
      * equivalent to {@link #addForceModel(ForceModel) add}
      * a {@link NewtonianAttraction} force model.
      * </p>
      * @param mu central attraction coefficient (m³/s²)
      * @see #addForceModel(ForceModel)
      * @see #getAllForceModels()
      */
     @Override
     public void setMu(final T mu) {
         if (ignoreCentralAttraction) {
             superSetMu(mu);
         } else {
             addForceModel(new NewtonianAttraction(mu.getReal()));
         }
     }
 
     /** Set the central attraction coefficient μ only in upper class.
      * @param mu central attraction coefficient (m³/s²)
      */
     private void superSetMu(final T mu) {
         super.setMu(mu);
     }
 
     /** Check if Newtonian attraction force model is available.
      * <p>
      * Newtonian attraction is always the last force model in the list.
      * </p>
      * @return true if Newtonian attraction force model is available
      */
     private boolean hasNewtonianAttraction() {
         final int last = forceModels.size() - 1;
         return last >= 0 && forceModels.get(last) instanceof NewtonianAttraction;
     }
 
     /** Add a force model to the global perturbation model.
      * <p>If this method is not called at all, the integrated orbit will follow
      * a Keplerian evolution only.</p>
      * @param model perturbing {@link ForceModel} to add
      * @see #removeForceModels()
      * @see #setMu(CalculusFieldElement)
      */
     public void addForceModel(final ForceModel model) {
 
         if (model instanceof final NewtonianAttraction na) {
             // we want to add the central attraction force model
 
             // ensure the state mapper knows about the new mu
             final T zero = getField().getZero();
             superSetMu(zero.newInstance(na.getMu()));
 
             // ensure we are notified of any mu change
             model.
                 getParametersDrivers().
                 getFirst().
                 addObserver((previousValue, driver) -> superSetMu(zero.newInstance(driver.getValue())));
 
             if (hasNewtonianAttraction()) {
                 // there is already a central attraction model, replace it
                 forceModels.set(forceModels.size() - 1, model);
             } else {
                 // there are no central attraction model yet, add it at the end of the list
                 forceModels.add(model);
             }
         } else {
             // we want to add a perturbing force model
             if (hasNewtonianAttraction()) {
                 // insert the new force model before Newtonian attraction,
                 // which should always be the last one in the list
                 forceModels.add(forceModels.size() - 1, model);
             } else {
                 // we only have perturbing force models up to now, just append at the end of the list
                 forceModels.add(model);
             }
         }
 
     }
 
     /** Remove all perturbing force models from the global perturbation model.
      * <p>Once all perturbing forces have been removed (and as long as no new force
      * model is added), the integrated orbit will follow a Keplerian evolution
      * only.</p>
      * @see #addForceModel(ForceModel)
      */
     public void removeForceModels() {
         forceModels.clear();
     }
 
     /** Get all the force models, perturbing forces and Newtonian attraction included.
      * @return list of perturbing force models, with Newtonian attraction being the
      * last one
      * @see #addForceModel(ForceModel)
      * @see #setMu(CalculusFieldElement)
      * @since 9.1
      */
     public List<ForceModel> getAllForceModels() {
         return Collections.unmodifiableList(forceModels);
     }
 
     /** Set propagation orbit type.
      * @param orbitParamsType orbit type to use for propagation
      */
     @Override
     public void setOrbitParamsType(final OrbitParamsType orbitParamsType) {
         super.setOrbitParamsType(orbitParamsType);
     }
 
     /** Get propagation parameter type.
      * @return orbit type used for propagation
      */
     @Override
     public OrbitParamsType getOrbitParamsType() {
         return superGetOrbitType();
     }
 
     /** Get propagation parameter type.
      * @return orbit type used for propagation
      */
     private OrbitParamsType superGetOrbitType() {
         return super.getOrbitParamsType();
     }
 
     /** Set position angle type.
      * <p>
      * The position parameter type is meaningful only if {@link
      * #getOrbitParamsType() propagation orbit type}
      * support it. As an example, it is not meaningful for propagation
      * in {@link OrbitParamsType#CARTESIAN Cartesian} parameters.
      * </p>
      * @param positionAngleType angle type to use for propagation
      */
     @Override
     public void setPositionAngleType(final PositionAngleType positionAngleType) {
         super.setPositionAngleType(positionAngleType);
     }
 
     /** Get propagation parameter type.
      * @return angle type to use for propagation
      */
     @Override
     public PositionAngleType getPositionAngleType() {
         return super.getPositionAngleType();
     }
 
     /** Set the initial state.
      * @param initialState initial state
      */
     public void setInitialState(final FieldSpacecraftState<T> initialState) {
         resetInitialState(initialState);
     }
 
     /** {@inheritDoc} */
     @Override
     public void resetInitialState(final FieldSpacecraftState<T> state) {
         super.resetInitialState(state);
         if (!hasNewtonianAttraction()) {
             setMu(state.getOrbit().getMu());
         }
         setStartDate(state.getDate());
     }
 
     /** {@inheritDoc} */
     @Override
     protected AttitudeProvider initializeAttitudeProviderForDerivatives() {
         return needFullAttitudeForDerivatives ? getAttitudeProvider() : getFrozenAttitudeProvider();
     }
 
     /** {@inheritDoc} */
     @Override
     protected FieldStateMapper<T> createMapper(final FieldAbsoluteDate<T> referenceDate, final T mu,
                                                final OrbitParamsType orbitParamsType, final PositionAngleType positionAngleType,
                                                final AttitudeProvider attitudeProvider, final Frame frame) {
         return new FieldOsculatingMapper(referenceDate, mu, orbitParamsType, positionAngleType, attitudeProvider, frame);
     }
 
     /** Internal mapper using directly osculating parameters. */
     private class FieldOsculatingMapper extends FieldStateMapper<T> {
 
         /** Simple constructor.
          * <p>
          * The position parameter type is meaningful only if {@link
          * #getOrbitParamsType() propagation orbit type}
          * support it. As an example, it is not meaningful for propagation
          * in {@link OrbitParamsType#CARTESIAN Cartesian} parameters.
          * </p>
          * @param referenceDate reference date
          * @param mu central attraction coefficient (m³/s²)
          * @param orbitParamsType orbit type to use for mapping
          * @param positionAngleType angle type to use for propagation
          * @param attitudeProvider attitude provider
          * @param frame inertial frame
          */
         FieldOsculatingMapper(final FieldAbsoluteDate<T> referenceDate, final T mu,
                               final OrbitParamsType orbitParamsType, final PositionAngleType positionAngleType,
                               final AttitudeProvider attitudeProvider, final Frame frame) {
             super(referenceDate, mu, orbitParamsType, positionAngleType, attitudeProvider, frame);
         }
 
         /** {@inheritDoc} */
         @Override
         public FieldSpacecraftState<T> mapArrayToState(final FieldAbsoluteDate<T> date, final T[] y, final T[] yDot,
                                                        final PropagationType type) {
             // the parameter type is ignored for the Numerical Propagator
 
             final T mass = y[6];
             final T massRate = yDot == null ? mass.getField().getZero() : yDot[6];
             if (mass.getReal() <= 0.0) {
                 throw new OrekitException(OrekitMessages.NOT_POSITIVE_SPACECRAFT_MASS, mass.getReal());
             }
 
             if (superGetOrbitType() == null) {
                 // propagation uses absolute position-velocity-acceleration
                 final FieldVector3D<T> p = new FieldVector3D<>(y[0],    y[1],    y[2]);
                 final FieldVector3D<T> v = new FieldVector3D<>(y[3],    y[4],    y[5]);
                 final FieldVector3D<T> a;
                 final FieldAbsolutePVCoordinates<T> absPva;
                 if (yDot == null) {
                     absPva = new FieldAbsolutePVCoordinates<>(getFrame(), new TimeStampedFieldPVCoordinates<>(date, p, v, FieldVector3D.getZero(date.getField())));
                 } else {
                     a = new FieldVector3D<>(yDot[3], yDot[4], yDot[5]);
                     absPva = new FieldAbsolutePVCoordinates<>(getFrame(), new TimeStampedFieldPVCoordinates<>(date, p, v, a));
                 }
 
                 final FieldAttitude<T> attitude = getAttitudeProvider().getAttitude(absPva, date, getFrame());
                 return new FieldSpacecraftState<>(absPva, attitude).withMassRate(massRate).withMass(mass);
             } else {
                 // propagation uses regular orbits
                 final FieldOrbit<T> orbit       = superGetOrbitType().mapArrayToOrbit(y, yDot, super.getPositionAngleType(), date, getMu(), getFrame());
                 final FieldAttitude<T> attitude = getAttitudeProvider().getAttitude(orbit, date, getFrame());
                 return new FieldSpacecraftState<>(orbit, attitude).withMassRate(massRate).withMass(mass);
             }
         }
 
         /** {@inheritDoc} */
         @Override
         public void mapStateToArray(final FieldSpacecraftState<T> state, final T[] y, final T[] yDot) {
             if (superGetOrbitType() == null) {
                 // propagation uses absolute position-velocity-acceleration
                 final FieldVector3D<T> p = state.getAbsPVA().getPosition();
                 final FieldVector3D<T> v = state.getAbsPVA().getVelocity();
                 y[0] = p.getX();
                 y[1] = p.getY();
                 y[2] = p.getZ();
                 y[3] = v.getX();
                 y[4] = v.getY();
                 y[5] = v.getZ();
             }
             else {
                 superGetOrbitType().mapOrbitToArray(state.getOrbit(), super.getPositionAngleType(), y, yDot);
             }
             y[6] = state.getMass();
         }
 
     }
 
     /** {@inheritDoc} */
     @Override
     protected MainStateEquations<T> getMainStateEquations(final FieldODEIntegrator<T> integrator) {
         return new Main(integrator);
     }
 
     /** Internal class for osculating parameters integration. */
     private class Main implements MainStateEquations<T>, FieldTimeDerivativesEquations<T> {
 
         /** Derivatives array. */
         private final T[] yDot;
 
         /** Current state. */
         private FieldSpacecraftState<T> currentState;
 
         /** Jacobian of the orbital parameters with respect to the Cartesian parameters. */
         private final T[][] jacobian;
 
         /** Flag keeping track whether Jacobian matrix needs to be recomputed or not. */
         private boolean recomputingJacobian;
 
         /** Simple constructor.
          * @param integrator numerical integrator to use for propagation.
          */
         Main(final FieldODEIntegrator<T> integrator) {
 
             this.yDot     = MathArrays.buildArray(getField(),  7);
             this.jacobian = MathArrays.buildArray(getField(),  6, 6);
             this.recomputingJacobian = true;
 
             // feed internal event detectors
             for (final ForceModel forceModel : forceModels) {
                 forceModel.getFieldEventDetectors(getField()).forEach(detector -> setUpEventDetector(integrator, detector));
             }
             getAttitudeProvider().getFieldEventDetectors(getField()).forEach(detector -> setUpEventDetector(integrator, detector));
 
             // default value for Jacobian is identity
             for (int i = 0; i < jacobian.length; ++i) {
                 Arrays.fill(jacobian[i], getField().getZero());
                 jacobian[i][i] = getField().getOne();
             }
 
         }
 
         /** {@inheritDoc} */
         @Override
         public void init(final FieldSpacecraftState<T> initialState, final FieldAbsoluteDate<T> target) {
             needFullAttitudeForDerivatives = forceModels.stream().anyMatch(ForceModel::dependsOnAttitudeRate);
 
             forceModels.forEach(fm -> fm.init(initialState, target));
 
             final int numberOfForces = forceModels.size();
             final OrbitParamsType orbitParamsType = superGetOrbitType();
             if (orbitParamsType != null && orbitParamsType != OrbitParamsType.CARTESIAN && numberOfForces > 0) {
                 if (numberOfForces > 1) {
                     recomputingJacobian = true;
                 } else {
                     recomputingJacobian = !(forceModels.getFirst() instanceof NewtonianAttraction);
                 }
             } else {
                 recomputingJacobian = false;
             }
         }
 
         /** {@inheritDoc} */
         @Override
         public T[] computeDerivatives(final FieldSpacecraftState<T> state) {
             final T zero = state.getMass().getField().getZero();
             currentState = state;
             Arrays.fill(yDot, zero);
             if (recomputingJacobian) {
                 // propagation uses Jacobian matrix of orbital parameters w.r.t. Cartesian ones
                 currentState.getOrbit().getJacobianWrtCartesian(getPositionAngleType(), jacobian);
             }
 
             // compute the contributions of all perturbing forces,
             // using the Kepler contribution at the end since
             // NewtonianAttraction is always the last instance in the list
             for (final ForceModel forceModel : forceModels) {
                 forceModel.addContribution(state, this);
             }
 
             if (superGetOrbitType() == null) {
                 // position derivative is velocity, and was not added above in the force models
                 // (it is added when orbit type is non-null because NewtonianAttraction considers it)
                 final FieldVector3D<T> velocity = currentState.getVelocity();
                 yDot[0] = yDot[0].add(velocity.getX());
                 yDot[1] = yDot[1].add(velocity.getY());
                 yDot[2] = yDot[2].add(velocity.getZ());
             }
 
             return yDot.clone();
 
         }
 
         /** {@inheritDoc} */
         @Override
         public void addKeplerContribution(final T mu) {
             if (superGetOrbitType() == null) {
 
                 // if mu is neither 0 nor NaN, we want to include Newtonian acceleration
                 if (mu.getReal() > 0) {
                     // velocity derivative is Newtonian acceleration
                     final FieldVector3D<T> position = currentState.getPosition();
                     final T r2         = position.getNorm2Sq();
                     final T coeff      = r2.multiply(r2.sqrt()).reciprocal().negate().multiply(mu);
                     yDot[3] = yDot[3].add(coeff.multiply(position.getX()));
                     yDot[4] = yDot[4].add(coeff.multiply(position.getY()));
                     yDot[5] = yDot[5].add(coeff.multiply(position.getZ()));
                 }
 
             } else {
                 // propagation uses regular orbits
                 currentState.getOrbit().addKeplerContribution(getPositionAngleType(), mu, yDot);
             }
         }
 
         /** {@inheritDoc} */
         @Override
         public void addNonKeplerianAcceleration(final FieldVector3D<T> gamma) {
             for (int i = 0; i < 6; ++i) {
                 final T[] jRow = jacobian[i];
                 yDot[i] = yDot[i].add(jRow[3].linearCombination(jRow[3], gamma.getX(),
                                                                 jRow[4], gamma.getY(),
                                                                 jRow[5], gamma.getZ()));
             }
         }
 
         /** {@inheritDoc} */
         @Override
         public void addMassDerivative(final T q) {
             if (q.getReal() > 0) {
                 throw new OrekitIllegalArgumentException(OrekitMessages.POSITIVE_FLOW_RATE, q.getReal());
             }
             yDot[6] = yDot[6].add(q);
         }
 
     }
 
 }