/*
 Copyright (C) 2008 Richard Gomes

 This source code is release under the BSD License.

 This file is part of JQuantLib, a free-software/open-source library
 for financial quantitative analysts and developers - http://jquantlib.org/

 JQuantLib is free software: you can redistribute it and/or modify it
 under the terms of the JQuantLib license.  You should have received a
 copy of the license along with this program; if not, please email
 . The license is also available online at
 .

 This program is distributed in the hope that it will be useful, but WITHOUT
 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 FOR A PARTICULAR PURPOSE.  See the license for more details.

 JQuantLib is based on QuantLib. http://quantlib.org/
 When applicable, the original copyright notice follows this notice.
 */

package org.jquantlib.math.integrals;

import org.jquantlib.lang.exceptions.LibraryException;
import org.jquantlib.math.Ops;

/**
 * @author 
 */
// TODO: code review :: license, class comments, comments for access modifiers, comments for @Override
public class TabulatedGaussLegendre {

    // Abscissas and Weights from Abramowitz and Stegun

    /* order 6 */
    private static final double x6[] = {
        0.238619186083197,
        0.661209386466265,
        0.932469514203152 };

    private static final double w6[] = {
        0.467913934572691,
        0.360761573048139,
        0.171324492379170 };

    private static final int n6 = 3;

    /* order 7 */
    private static final double x7[] = {
        0.000000000000000,
        0.405845151377397,
        0.741531185599394,
        0.949107912342759 };

    private static final double w7[] = {
        0.417959183673469,
        0.381830050505119,
        0.279705391489277,
        0.129484966168870 };

    private static final int n7 = 4;

    /* order 12 */
    private static final double x12[] = {
        0.125233408511469,
        0.367831498998180,
        0.587317954286617,
        0.769902674194305,
        0.904117256370475,
        0.981560634246719 };

    private static final double w12[] = {
        0.249147045813403,
        0.233492536538355,
        0.203167426723066,
        0.160078328543346,
        0.106939325995318,
        0.047175336386512 };

    private static final int n12 = 6;

    /* order 20 */
    private static final double x20[] = {
        0.076526521133497,
        0.227785851141645,
        0.373706088715420,
        0.510867001950827,
        0.636053680726515,
        0.746331906460151,
        0.839116971822219,
        0.912234428251326,
        0.963971927277914,
        0.993128599185095 };

    private static final double w20[] = {
        0.152753387130726,
        0.149172986472604,
        0.142096109318382,
        0.131688638449177,
        0.118194531961518,
        0.101930119817240,
        0.083276741576704,
        0.062672048334109,
        0.040601429800387,
        0.017614007139152 };

    private static final int n20 = 10;

    private int order_;
    private double[] x_;
    private double[] w_;
    private int n_;


    public TabulatedGaussLegendre() {
        setOrder(20);
    }

    public TabulatedGaussLegendre(final int order){
        setOrder(order);
    }

    public double evaluate(final Ops.DoubleOp f) {

        int startIdx;
        double val;

        final boolean isOrderOdd = ((order_ & 1) != 0);

        if (w_ == null)
            throw new ArithmeticException("null weights");
        if (x_ == null)
            throw new ArithmeticException("null abscissas");

        if (isOrderOdd) {
            if (!(n_ > 0))
                throw new ArithmeticException("assume at least 1 point in quadrature");
            val = w_[0]*f.op(x_[0]);
            startIdx=1;
        } else {
            val = 0.0;
            startIdx=0;
        }

        for (int i=startIdx; i