RcFieldDuplication.java

/*
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 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The Hipparchus project licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
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 *
 *      https://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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 * See the License for the specific language governing permissions and
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package org.hipparchus.special.elliptic.carlson;

import org.hipparchus.CalculusFieldElement;
import org.hipparchus.complex.Complex;
import org.hipparchus.complex.FieldComplex;
import org.hipparchus.util.FastMath;

/** Duplication algorithm for Carlson R<sub>C</sub> elliptic integral.
 * @param <T> type of the field elements (really {@link Complex} or {@link FieldComplex})
 * @since 2.0
 */
class RcFieldDuplication<T extends CalculusFieldElement<T>> extends FieldDuplication<T> {

    /** Simple constructor.
     * @param x first symmetric variable of the integral
     * @param y second symmetric variable of the integral
     */
    RcFieldDuplication(final T x, final T y) {
        super(x, y);
    }

    /** {@inheritDoc} */
    @Override
    protected void initialMeanPoint(final T[] va) {
        va[2] = va[0].add(va[1].multiply(2)).divide(3.0);
    }

    /** {@inheritDoc} */
    @Override
    protected T convergenceCriterion(final T r, final T max) {
        return max.divide(FastMath.sqrt(FastMath.sqrt(FastMath.sqrt(r.multiply(3.0)))));
    }

    /** {@inheritDoc} */
    @Override
    protected void update(final int m, final T[] vaM, final T[] sqrtM, final  double fourM) {
        final T lambdaA = sqrtM[0].multiply(sqrtM[1]).multiply(2);
        final T lambdaB = vaM[1];
        vaM[0] = vaM[0].linearCombination(0.25, vaM[0], 0.25, lambdaA, 0.25, lambdaB); // xₘ
        vaM[1] = vaM[1].linearCombination(0.25, vaM[1], 0.25, lambdaA, 0.25, lambdaB); // yₘ
        vaM[2] = vaM[2].linearCombination(0.25, vaM[2], 0.25, lambdaA, 0.25, lambdaB); // aₘ
    }

    /** {@inheritDoc} */
    @Override
    protected T evaluate(final T[] va0, final T aM, final  double fourM) {

        // compute the single polynomial independent variable
        final T s = va0[1].subtract(va0[2]).divide(aM.multiply(fourM));

        // evaluate integral using equation 2.13 in Carlson[1995]
        final T poly = s.multiply(RcRealDuplication.S7).
                       add(RcRealDuplication.S6).multiply(s).
                       add(RcRealDuplication.S5).multiply(s).
                       add(RcRealDuplication.S4).multiply(s).
                       add(RcRealDuplication.S3).multiply(s).
                       add(RcRealDuplication.S2).multiply(s).
                       multiply(s).
                       add(RcRealDuplication.S0).
                       divide(RcRealDuplication.DENOMINATOR);
        return poly.divide(FastMath.sqrt(aM));

    }

}