PolynomialAccelerationModel.java
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*
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package org.orekit.forces.empirical;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.util.FastMath;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ParameterDriver;
/** Polynomial acceleration model.
* @since 10.3
* @author Luc Maisonobe
* @author Bryan Cazabonne
*/
public class PolynomialAccelerationModel implements AccelerationModel {
/** Acceleration scaling factor.
* <p>
* 2⁻²⁰ is the order of magnitude of third body perturbing acceleration.
* </p>
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private static final double ACCELERATION_SCALE = FastMath.scalb(1.0, -20);
/** Drivers for the polynomial coefficients. */
private final List<ParameterDriver> drivers;
/** Reference date for computing polynomials. */
private AbsoluteDate referenceDate;
/** Simple constructor.
* @param prefix prefix to use for parameter drivers
* @param referenceDate reference date for computing polynomials, if null
* the reference date will be automatically set at propagation start
* @param degree polynomial degree (i.e. a value of 0 corresponds to a constant acceleration)
*/
public PolynomialAccelerationModel(final String prefix,
final AbsoluteDate referenceDate,
final int degree) {
// Reference date
this.referenceDate = referenceDate;
// Parameter drivers
drivers = new ArrayList<>();
for (int i = 0; i < degree + 1; ++i) {
drivers.add(new ParameterDriver(prefix + "[" + i + "]", 0.0, ACCELERATION_SCALE,
Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY));
}
}
/** {@inheritDoc} */
@Override
public void init(final SpacecraftState initialState, final AbsoluteDate target) {
if (referenceDate == null) {
referenceDate = initialState.getDate();
}
}
/** {@inheritDoc} */
@Override
public double signedAmplitude(final SpacecraftState state,
final double[] parameters) {
final double dt = state.getDate().durationFrom(referenceDate);
double amplitude = 0;
for (int i = parameters.length - 1; i >= 0; --i) {
amplitude += amplitude * dt + parameters[i];
}
return amplitude;
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> T signedAmplitude(final FieldSpacecraftState<T> state,
final T[] parameters) {
final T dt = state.getDate().durationFrom(referenceDate);
T amplitude = dt.getField().getZero();
for (int i = parameters.length - 1; i >= 0; --i) {
amplitude = amplitude.add(amplitude.multiply(dt).add(parameters[i]));
}
return amplitude;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return Collections.unmodifiableList(drivers);
}
}