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 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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.
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package org.apache.commons.math3.analysis.interpolation;

import org.apache.commons.math3.analysis.UnivariateFunction;
import org.apache.commons.math3.util.MathUtils;
import org.apache.commons.math3.util.MathArrays;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.NonMonotonicSequenceException;
import org.apache.commons.math3.exception.NumberIsTooSmallException;

Adapter for classes implementing the UnivariateInterpolator interface. The data to be interpolated is assumed to be periodic. Thus values that are outside of the range can be passed to the interpolation function: They will be wrapped into the initial range before being passed to the class that actually computes the interpolation. /**
 * Adapter for classes implementing the {@link UnivariateInterpolator}
 * interface.
 * The data to be interpolated is assumed to be periodic. Thus values that are
 * outside of the range can be passed to the interpolation function: They will
 * be wrapped into the initial range before being passed to the class that
 * actually computes the interpolation.
 *
 */
public class UnivariatePeriodicInterpolator
    implements UnivariateInterpolator {
    
Default number of extension points of the samples array. /** Default number of extension points of the samples array. */
    public static final int DEFAULT_EXTEND = 5;
    
Interpolator. /** Interpolator. */
    private final UnivariateInterpolator interpolator;
    
Period. /** Period. */
    private final double period;
    
Number of extension points. /** Number of extension points. */
    private final int extend;

    
Builds an interpolator.
Params:
interpolator – Interpolator.
period – Period.
extend – Number of points to be appended at the beginning and end of the sample arrays in order to avoid interpolation failure at the (periodic) boundaries of the orginal interval. The value is the number of sample points which the original interpolator needs on each side of the interpolated point./**
     * Builds an interpolator.
     *
     * @param interpolator Interpolator.
     * @param period Period.
     * @param extend Number of points to be appended at the beginning and
     * end of the sample arrays in order to avoid interpolation failure at
     * the (periodic) boundaries of the orginal interval. The value is the
     * number of sample points which the original {@code interpolator} needs
     * on each side of the interpolated point.
     */
    public UnivariatePeriodicInterpolator(UnivariateInterpolator interpolator,
                                          double period,
                                          int extend) {
        this.interpolator = interpolator;
        this.period = period;
        this.extend = extend;
    }

    
Builds an interpolator. Uses DEFAULT_EXTEND as the number of extension points on each side of the original abscissae range. 
Params:
interpolator – Interpolator.
period – Period./**
     * Builds an interpolator.
     * Uses {@link #DEFAULT_EXTEND} as the number of extension points on each side
     * of the original abscissae range.
     *
     * @param interpolator Interpolator.
     * @param period Period.
     */
    public UnivariatePeriodicInterpolator(UnivariateInterpolator interpolator,
                                          double period) {
        this(interpolator, period, DEFAULT_EXTEND);
    }

    
{@inheritDoc}
Throws:
NumberIsTooSmallException – if the number of extension points is larger than the size of xval./**
     * {@inheritDoc}
     *
     * @throws NumberIsTooSmallException if the number of extension points
     * is larger than the size of {@code xval}.
     */
    public UnivariateFunction interpolate(double[] xval,
                                          double[] yval)
        throws NumberIsTooSmallException, NonMonotonicSequenceException {
        if (xval.length < extend) {
            throw new NumberIsTooSmallException(xval.length, extend, true);
        }

        MathArrays.checkOrder(xval);
        final double offset = xval[0];

        final int len = xval.length + extend * 2;
        final double[] x = new double[len];
        final double[] y = new double[len];
        for (int i = 0; i < xval.length; i++) {
            final int index = i + extend;
            x[index] = MathUtils.reduce(xval[i], period, offset);
            y[index] = yval[i];
        }

        // Wrap to enable interpolation at the boundaries.
        for (int i = 0; i < extend; i++) {
            int index = xval.length - extend + i;
            x[i] = MathUtils.reduce(xval[index], period, offset) - period;
            y[i] = yval[index];

            index = len - extend + i;
            x[index] = MathUtils.reduce(xval[i], period, offset) + period;
            y[index] = yval[i];
        }

        MathArrays.sortInPlace(x, y);

        final UnivariateFunction f = interpolator.interpolate(x, y);
        return new UnivariateFunction() {
            
{@inheritDoc} /** {@inheritDoc} */
            public double value(final double x) throws MathIllegalArgumentException {
                return f.value(MathUtils.reduce(x, period, offset));
            }
        };
    }
}