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/* -*- mode: c++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */

 Copyright (C) 2005 StatPro Italia srl

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

 QuantLib is free software: you can redistribute it and/or modify it
 under the terms of the QuantLib license.  You should have received a
 copy of the license along with this program; if not, please email
 <quantlib-dev@lists.sf.net>. 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.

/*! \file backwardflatinterpolation.hpp
    \brief backward-flat interpolation between discrete points

#ifndef quantlib_backward_flat_interpolation_hpp
#define quantlib_backward_flat_interpolation_hpp

#include <ql/Math/interpolation.hpp>
#include <vector>

namespace QuantLib {

    namespace detail {

        template <class I1, class I2>
        class BackwardFlatInterpolationImpl
            : public Interpolation::templateImpl<I1,I2> {
            BackwardFlatInterpolationImpl(const I1& xBegin, const I1& xEnd,
                                          const I2& yBegin)
            : Interpolation::templateImpl<I1,I2>(xBegin,xEnd,yBegin),
              primitive_(xEnd-xBegin) {
            void calculate() {
                Size n = this->xEnd_-this->xBegin_;
                primitive_[0] = 0.0;
                for (Size i=1; i<n; i++) {
                    Real dx = this->xBegin_[i]-this->xBegin_[i-1];
                    primitive_[i] = primitive_[i-1] + dx*this->yBegin_[i];
            Real value(Real x) const {
                Size i = this->locate(x);
                if (x == this->xBegin_[i])
                    return this->yBegin_[i];
                    return this->yBegin_[i+1];
            Real primitive(Real x) const {
                Size i = this->locate(x);
                Real dx = x-this->xBegin_[i];
                return primitive_[i] + dx*this->yBegin_[i+1];
            Real derivative(Real) const {
                return 0.0;
            Real secondDerivative(Real) const {
                return 0.0;
            std::vector<Real> primitive_;


    //! Backward-flat interpolation between discrete points
00077     class BackwardFlatInterpolation : public Interpolation {
        /*! \pre the \f$ x \f$ values must be sorted. */
        template <class I1, class I2>
00081         BackwardFlatInterpolation(const I1& xBegin, const I1& xEnd,
                                  const I2& yBegin) {
            impl_ = boost::shared_ptr<Interpolation::Impl>(
                new detail::BackwardFlatInterpolationImpl<I1,I2>(xBegin, xEnd,

    //! Backward-flat interpolation factory and traits
00090     class BackwardFlat {
        template <class I1, class I2>
        Interpolation interpolate(const I1& xBegin, const I1& xEnd,
                                  const I2& yBegin) const {
            return BackwardFlatInterpolation(xBegin,xEnd,yBegin);
        enum { global = 0 };



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