Java example source code file (FieldHermiteInterpolator.java)

This example Java source code file (FieldHermiteInterpolator.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, dimensionmismatchexception, fieldelement, fieldhermiteinterpolator, list, matharithmeticexception, nodataexception, nullargumentexception, util, zeroexception

The FieldHermiteInterpolator.java Java example source code

/*
 * 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.
 */
package org.apache.commons.math3.analysis.interpolation;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.math3.FieldElement;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MathArithmeticException;
import org.apache.commons.math3.exception.NoDataException;
import org.apache.commons.math3.exception.NullArgumentException;
import org.apache.commons.math3.exception.ZeroException;
import org.apache.commons.math3.exception.util.LocalizedFormats;
import org.apache.commons.math3.util.MathArrays;
import org.apache.commons.math3.util.MathUtils;

/** Polynomial interpolator using both sample values and sample derivatives.
 * <p>
 * The interpolation polynomials match all sample points, including both values
 * and provided derivatives. There is one polynomial for each component of
 * the values vector. All polynomials have the same degree. The degree of the
 * polynomials depends on the number of points and number of derivatives at each
 * point. For example the interpolation polynomials for n sample points without
 * any derivatives all have degree n-1. The interpolation polynomials for n
 * sample points with the two extreme points having value and first derivative
 * and the remaining points having value only all have degree n+1. The
 * interpolation polynomial for n sample points with value, first and second
 * derivative for all points all have degree 3n-1.
 * </p>
 *
 * @param <T> Type of the field elements.
 *
 * @since 3.2
 */
public class FieldHermiteInterpolator<T extends FieldElement {

    /** Sample abscissae. */
    private final List<T> abscissae;

    /** Top diagonal of the divided differences array. */
    private final List<T[]> topDiagonal;

    /** Bottom diagonal of the divided differences array. */
    private final List<T[]> bottomDiagonal;

    /** Create an empty interpolator.
     */
    public FieldHermiteInterpolator() {
        this.abscissae      = new ArrayList<T>();
        this.topDiagonal    = new ArrayList<T[]>();
        this.bottomDiagonal = new ArrayList<T[]>();
    }

    /** Add a sample point.
     * <p>
     * This method must be called once for each sample point. It is allowed to
     * mix some calls with values only with calls with values and first
     * derivatives.
     * </p>
     * <p>
     * The point abscissae for all calls <em>must be different.
     * </p>
     * @param x abscissa of the sample point
     * @param value value and derivatives of the sample point
     * (if only one row is passed, it is the value, if two rows are
     * passed the first one is the value and the second the derivative
     * and so on)
     * @exception ZeroException if the abscissa difference between added point
     * and a previous point is zero (i.e. the two points are at same abscissa)
     * @exception MathArithmeticException if the number of derivatives is larger
     * than 20, which prevents computation of a factorial
     * @throws DimensionMismatchException if derivative structures are inconsistent
     * @throws NullArgumentException if x is null
     */
    public void addSamplePoint(final T x, final T[] ... value)
        throws ZeroException, MathArithmeticException,
               DimensionMismatchException, NullArgumentException {

        MathUtils.checkNotNull(x);
        T factorial = x.getField().getOne();
        for (int i = 0; i < value.length; ++i) {

            final T[] y = value[i].clone();
            if (i > 1) {
                factorial = factorial.multiply(i);
                final T inv = factorial.reciprocal();
                for (int j = 0; j < y.length; ++j) {
                    y[j] = y[j].multiply(inv);
                }
            }

            // update the bottom diagonal of the divided differences array
            final int n = abscissae.size();
            bottomDiagonal.add(n - i, y);
            T[] bottom0 = y;
            for (int j = i; j < n; ++j) {
                final T[] bottom1 = bottomDiagonal.get(n - (j + 1));
                if (x.equals(abscissae.get(n - (j + 1)))) {
                    throw new ZeroException(LocalizedFormats.DUPLICATED_ABSCISSA_DIVISION_BY_ZERO, x);
                }
                final T inv = x.subtract(abscissae.get(n - (j + 1))).reciprocal();
                for (int k = 0; k < y.length; ++k) {
                    bottom1[k] = inv.multiply(bottom0[k].subtract(bottom1[k]));
                }
                bottom0 = bottom1;
            }

            // update the top diagonal of the divided differences array
            topDiagonal.add(bottom0.clone());

            // update the abscissae array
            abscissae.add(x);

        }

    }

    /** Interpolate value at a specified abscissa.
     * @param x interpolation abscissa
     * @return interpolated value
     * @exception NoDataException if sample is empty
     * @throws NullArgumentException if x is null
     */
    public T[] value(T x) throws NoDataException, NullArgumentException {

        // safety check
        MathUtils.checkNotNull(x);
        if (abscissae.isEmpty()) {
            throw new NoDataException(LocalizedFormats.EMPTY_INTERPOLATION_SAMPLE);
        }

        final T[] value = MathArrays.buildArray(x.getField(), topDiagonal.get(0).length);
        T valueCoeff = x.getField().getOne();
        for (int i = 0; i < topDiagonal.size(); ++i) {
            T[] dividedDifference = topDiagonal.get(i);
            for (int k = 0; k < value.length; ++k) {
                value[k] = value[k].add(dividedDifference[k].multiply(valueCoeff));
            }
            final T deltaX = x.subtract(abscissae.get(i));
            valueCoeff = valueCoeff.multiply(deltaX);
        }

        return value;

    }

    /** Interpolate value and first derivatives at a specified abscissa.
     * @param x interpolation abscissa
     * @param order maximum derivation order
     * @return interpolated value and derivatives (value in row 0,
     * 1<sup>st derivative in row 1, ... nth derivative in row n)
     * @exception NoDataException if sample is empty
     * @throws NullArgumentException if x is null
     */
    public T[][] derivatives(T x, int order) throws NoDataException, NullArgumentException {

        // safety check
        MathUtils.checkNotNull(x);
        if (abscissae.isEmpty()) {
            throw new NoDataException(LocalizedFormats.EMPTY_INTERPOLATION_SAMPLE);
        }

        final T zero = x.getField().getZero();
        final T one  = x.getField().getOne();
        final T[] tj = MathArrays.buildArray(x.getField(), order + 1);
        tj[0] = zero;
        for (int i = 0; i < order; ++i) {
            tj[i + 1] = tj[i].add(one);
        }

        final T[][] derivatives =
                MathArrays.buildArray(x.getField(), order + 1, topDiagonal.get(0).length);
        final T[] valueCoeff = MathArrays.buildArray(x.getField(), order + 1);
        valueCoeff[0] = x.getField().getOne();
        for (int i = 0; i < topDiagonal.size(); ++i) {
            T[] dividedDifference = topDiagonal.get(i);
            final T deltaX = x.subtract(abscissae.get(i));
            for (int j = order; j >= 0; --j) {
                for (int k = 0; k < derivatives[j].length; ++k) {
                    derivatives[j][k] =
                            derivatives[j][k].add(dividedDifference[k].multiply(valueCoeff[j]));
                }
                valueCoeff[j] = valueCoeff[j].multiply(deltaX);
                if (j > 0) {
                    valueCoeff[j] = valueCoeff[j].add(tj[j].multiply(valueCoeff[j - 1]));
                }
            }
        }

        return derivatives;

    }

}