FieldCjSjCoefficient.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.Field;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.complex.Complex;
import org.hipparchus.exception.NullArgumentException;
/** 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.
* @param <T> type of the field elements
*/
public class FieldCjSjCoefficient <T extends CalculusFieldElement<T>> {
/** Zero for initialization. /*/
private final T zero;
/** Last computed order j. */
private int jLast;
/** Complex base (k + ih) of the C<sub>j</sub>, S<sub>j</sub> series. */
private final FieldComplex<T> kih;
/** List of computed elements. */
private final List<FieldComplex<T>> cjsj;
/** C<sub>j</sub>(k, h) and S<sub>j</sub>(k, h) constructor.
* @param k k value
* @param h h value
* @param field field for fieldElements
*/
public FieldCjSjCoefficient(final T k, final T h, final Field<T> field) {
zero = field.getZero();
kih = new FieldComplex<>(k, h);
cjsj = new ArrayList<FieldComplex<T>>();
cjsj.add(new FieldComplex<>(zero.add(1.), zero));
cjsj.add(kih);
jLast = 1;
}
/** Get the C<sub>j</sub> coefficient.
* @param j order
* @return C<sub>j</sub>
*/
public T 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 T 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 T getDcjDk(final int j) {
return j == 0 ? zero : getCj(j - 1).multiply(j);
}
/** Get the dS<sub>j</sub> / dk coefficient.
* @param j order
* @return dS<sub>j</sub> / d<sub>k</sub>
*/
public T getDsjDk(final int j) {
return j == 0 ? zero : getSj(j - 1).multiply(j);
}
/** Get the dC<sub>j</sub> / dh coefficient.
* @param j order
* @return dC<sub>i</sub> / d<sub>k</sub>
*/
public T getDcjDh(final int j) {
return j == 0 ? zero : getSj(j - 1).multiply(-j);
}
/** Get the dS<sub>j</sub> / dh coefficient.
* @param j order
* @return dS<sub>j</sub> / d<sub>h</sub>
*/
public T getDsjDh(final int j) {
return j == 0 ? zero : getCj(j - 1).multiply(j);
}
/** Update the cjsj up to order j.
* @param j order
*/
private void updateCjSj(final int j) {
FieldComplex<T> last = cjsj.get(cjsj.size() - 1);
for (int i = jLast; i < j; i++) {
final FieldComplex<T> next = last.multiply(kih);
cjsj.add(next);
last = next;
}
jLast = j;
}
private static class FieldComplex <T extends CalculusFieldElement<T>> {
/** The imaginary part. */
private final T imaginary;
/** The real part. */
private final T real;
/**
* Create a complex number given the real and imaginary parts.
*
* @param real Real part.
* @param imaginary Imaginary part.
*/
FieldComplex(final T real, final T imaginary) {
this.real = real;
this.imaginary = imaginary;
}
/**
* Access the real part.
*
* @return the real part.
*/
public T getReal() {
return real;
}
/**
* Access the imaginary part.
*
* @return the imaginary part.
*/
public T getImaginary() {
return imaginary;
}
/**
* Create a complex number given the real and imaginary parts.
*
* @param realPart Real part.
* @param imaginaryPart Imaginary part.
* @return a new complex number instance.
*
* @see #valueOf(double, double)
*/
protected FieldComplex<T> createComplex(final T realPart, final T imaginaryPart) {
return new FieldComplex<>(realPart, imaginaryPart);
}
/**
* Returns a {@code Complex} whose value is {@code this * factor}.
* Implements preliminary checks for {@code NaN} and infinity followed by
* the definitional formula:
* <p>
* {@code (a + bi)(c + di) = (ac - bd) + (ad + bc)i}
* </p>
* <p>
* Returns finite values in components of the result per the definitional
* formula in all remaining cases.</p>
*
* @param factor value to be multiplied by this {@code Complex}.
* @return {@code this * factor}.
* @throws NullArgumentException if {@code factor} is {@code null}.
*/
public FieldComplex<T> multiply(final FieldComplex<T> factor) throws NullArgumentException {
return createComplex(real.multiply(factor.real).subtract(imaginary.multiply(factor.imaginary)),
real.multiply(factor.imaginary).add(imaginary.multiply(factor.real)));
}
}
}