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OREKIT (ORbits Extrapolation KIT) is a low level space dynamics library. It provides basic elements (orbits, dates, attitude, frames ...) and various algorithms to handle them (conversions, analytical and numerical propagation, pointing ...).

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/* Copyright 2002-2021 CS GROUP
 * 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,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.orekit.data;

import java.io.Serializable;

import org.hipparchus.CalculusFieldElement;
import org.orekit.utils.Constants;

/**
 * Polynomial nutation function.
 *
 * @author Luc Maisonobe
 * @see PoissonSeries
 */
public class PolynomialNutation implements Serializable {

    /** Serializable UID. */
    private static final long serialVersionUID = 20131007L;

    /** Coefficients of the polynomial part. */
    private double[] coefficients;

    /** Build a polynomial from its coefficients.
     * @param coefficients polynomial coefficients in increasing degree
     */
    public PolynomialNutation(final double... coefficients) {
        this.coefficients = coefficients.clone();
    }

    /** Evaluate the value of the polynomial.
     * @param tc date offset in Julian centuries
     * @return value of the polynomial
     */
    public double value(final double tc) {

        double p = 0;
        for (int i = coefficients.length - 1; i >= 0; --i) {
            p = p * tc + coefficients[i];
        }

        return p;

    }

    /** Evaluate the time derivative of the polynomial.
     * @param tc date offset in Julian centuries
     * @return time derivative of the polynomial
     */
    public double derivative(final double tc) {

        double p = 0;
        for (int i = coefficients.length - 1; i > 0; --i) {
            p = p * tc + i * coefficients[i];
        }

        return p / Constants.JULIAN_CENTURY;

    }

    /** Evaluate the value of the polynomial.
     * @param tc date offset in Julian centuries
     * @param  type of the filed elements
     * @return value of the polynomial
     */
    public > T value(final T tc) {

        T p = tc.getField().getZero();
        for (int i = coefficients.length - 1; i >= 0; --i) {
            p = p.multiply(tc).add(coefficients[i]);
        }

        return p;

    }

    /** Evaluate the time derivative of the polynomial.
     * @param tc date offset in Julian centuries
     * @param  type of the filed elements
     * @return time derivative of the polynomial
     */
    public > T derivative(final T tc) {

        T p = tc.getField().getZero();
        for (int i = coefficients.length - 1; i > 0; --i) {
            p = p.multiply(tc).add( i * coefficients[i]);
        }

        return p.divide(Constants.JULIAN_CENTURY);

    }

}