CjSjCoefficient.java
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*
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package org.orekit.propagation.semianalytical.dsst.utilities;
import java.util.ArrayList;
import java.util.List;
import org.hipparchus.complex.Complex;
/** Compute the S<sub>j</sub>(k, h) and the C<sub>j</sub>(k, h) series
* and their partial derivatives with respect to k and h.
* <p>
* Those series are given in Danielson paper by expression 2.5.3-(5):
*
* <p> C<sub>j</sub>(k, h) + i S<sub>j</sub>(k, h) = (k+ih)<sup>j</sup>
*
* <p>
* The C<sub>j</sub>(k, h) and the S<sub>j</sub>(k, h) elements are store as an
* {@link ArrayList} of {@link Complex} number, the C<sub>j</sub>(k, h) being
* represented by the real and the S<sub>j</sub>(k, h) by the imaginary part.
*/
public class CjSjCoefficient {
/** Last computed order j. */
private int jLast;
/** Complex base (k + ih) of the C<sub>j</sub>, S<sub>j</sub> series. */
private final Complex kih;
/** List of computed elements. */
private final List<Complex> cjsj;
/** C<sub>j</sub>(k, h) and S<sub>j</sub>(k, h) constructor.
* @param k k value
* @param h h value
*/
public CjSjCoefficient(final double k, final double h) {
kih = new Complex(k, h);
cjsj = new ArrayList<Complex>();
cjsj.add(new Complex(1, 0));
cjsj.add(kih);
jLast = 1;
}
/** Get the C<sub>j</sub> coefficient.
* @param j order
* @return C<sub>j</sub>
*/
public double getCj(final int j) {
if (j > jLast) {
// Update to order j
updateCjSj(j);
}
return cjsj.get(j).getReal();
}
/** Get the S<sub>j</sub> coefficient.
* @param j order
* @return S<sub>j</sub>
*/
public double getSj(final int j) {
if (j > jLast) {
// Update to order j
updateCjSj(j);
}
return cjsj.get(j).getImaginary();
}
/** Get the dC<sub>j</sub> / dk coefficient.
* @param j order
* @return dC<sub>j</sub> / d<sub>k</sub>
*/
public double getDcjDk(final int j) {
return j == 0 ? 0 : j * getCj(j - 1);
}
/** Get the dS<sub>j</sub> / dk coefficient.
* @param j order
* @return dS<sub>j</sub> / d<sub>k</sub>
*/
public double getDsjDk(final int j) {
return j == 0 ? 0 : j * getSj(j - 1);
}
/** Get the dC<sub>j</sub> / dh coefficient.
* @param j order
* @return dC<sub>i</sub> / d<sub>k</sub>
*/
public double getDcjDh(final int j) {
return j == 0 ? 0 : -j * getSj(j - 1);
}
/** Get the dS<sub>j</sub> / dh coefficient.
* @param j order
* @return dS<sub>j</sub> / d<sub>h</sub>
*/
public double getDsjDh(final int j) {
return j == 0 ? 0 : j * getCj(j - 1);
}
/** Update the cjsj up to order j.
* @param j order
*/
private void updateCjSj(final int j) {
Complex last = cjsj.get(cjsj.size() - 1);
for (int i = jLast; i < j; i++) {
final Complex next = last.multiply(kih);
cjsj.add(next);
last = next;
}
jLast = j;
}
}