NegativeParameter.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
 * the License.  You may obtain a copy of the License at
 *
 *      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,
 * 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.
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package org.hipparchus.special.elliptic.jacobi;

import org.hipparchus.util.FastMath;

/** Algorithm for computing the principal Jacobi functions for negative parameter m.
 * <p>
 * The rules for negative parameter change are given in Abramowitz and Stegun, section 16.10.
 * </p>
 * @since 2.0
 */
class NegativeParameter extends JacobiElliptic {

    /** Algorithm to use for the positive parameter. */
    private final JacobiElliptic algorithm;

    /** Input scaling factor. */
    private final double inputScale;

    /** output scaling factor. */
    private final double outputScale;

    /** Simple constructor.
     * @param m parameter of the Jacobi elliptic function (must be negative here)
     */
    NegativeParameter(final double m) {
        super(m);
        final double omM = 1.0 - m;
        algorithm        = JacobiEllipticBuilder.build(-m / omM);
        inputScale       = FastMath.sqrt(omM);
        outputScale      = 1.0 / inputScale;
    }

    /** {@inheritDoc} */
    @Override
    public CopolarN valuesN(final double u) {
        final CopolarD trioD = new CopolarD(algorithm.valuesN(u * inputScale));
        return new CopolarN(outputScale * trioD.sd(), trioD.cd(), trioD.nd());
    }

}