com.opengamma.analytics.math.function.special.LegendrePolynomialFunction.java Source code

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Here is the source code for com.opengamma.analytics.math.function.special.LegendrePolynomialFunction.java

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/**
 * Copyright (C) 2009 - present by OpenGamma Inc. and the OpenGamma group of companies
 *
 * Please see distribution for license.
 */
package com.opengamma.analytics.math.function.special;

import org.apache.commons.lang.Validate;

import com.opengamma.analytics.math.function.DoubleFunction1D;
import com.opengamma.util.tuple.Pair;

/**
 * 
 */
public class LegendrePolynomialFunction extends OrthogonalPolynomialFunctionGenerator {

    @Override
    public DoubleFunction1D[] getPolynomials(final int n) {
        Validate.isTrue(n >= 0);
        final DoubleFunction1D[] polynomials = new DoubleFunction1D[n + 1];
        for (int i = 0; i <= n; i++) {
            if (i == 0) {
                polynomials[i] = getOne();
            } else if (i == 1) {
                polynomials[i] = getX();
            } else {
                polynomials[i] = (polynomials[i - 1].multiply(getX()).multiply(2 * i - 1)
                        .subtract(polynomials[i - 2].multiply(i - 1))).multiply(1. / i);
            }
        }
        return polynomials;
    }

    @Override
    public Pair<DoubleFunction1D, DoubleFunction1D>[] getPolynomialsAndFirstDerivative(final int n) {
        Validate.isTrue(n >= 0);
        @SuppressWarnings("unchecked")
        final Pair<DoubleFunction1D, DoubleFunction1D>[] polynomials = new Pair[n + 1];
        DoubleFunction1D p, dp;
        for (int i = 0; i <= n; i++) {
            if (i == 0) {
                polynomials[i] = Pair.of(getOne(), getZero());
            } else if (i == 1) {
                polynomials[i] = Pair.of(getX(), getOne());
            } else {
                p = (polynomials[i - 1].getFirst().multiply(getX()).multiply(2 * i - 1)
                        .subtract(polynomials[i - 2].getFirst().multiply(i - 1))).multiply(1. / i);
                dp = p.derivative();
                polynomials[i] = Pair.of(p, dp);
            }
        }
        return polynomials;
    }
}