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

/*

 Copyright (C) 2001, 2002, 2003 Sadruddin Rejeb

 Copyright (C) 2003 Ferdinando Ametrano

 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

 <https://www.quantlib.org/license.shtml>.

 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.

*/

#include <ql/methods/lattices/binomialtree.hpp>

#include <ql/stochasticprocess.hpp>

namespace QuantLib {

    JarrowRudd::JarrowRudd(

                        const ext::shared_ptr<StochasticProcess1D>& process,

                        Time end, Size steps, Real)

    : EqualProbabilitiesBinomialTree<JarrowRudd>(process, end, steps) {

        // drift removed

        up_ = process->stdDeviation(0.0, x0_, dt_);

    }

    CoxRossRubinstein::CoxRossRubinstein(

                        const ext::shared_ptr<StochasticProcess1D>& process,

                        Time end, Size steps, Real)

    : EqualJumpsBinomialTree<CoxRossRubinstein>(process, end, steps) {

        dx_ = process->stdDeviation(0.0, x0_, dt_);

        pu_ = 0.5 + 0.5*driftPerStep_/dx_;;

        pd_ = 1.0 - pu_;

        QL_REQUIRE(pu_<=1.0, "negative probability");

        QL_REQUIRE(pu_>=0.0, "negative probability");

    }

    AdditiveEQPBinomialTree::AdditiveEQPBinomialTree(

                        const ext::shared_ptr<StochasticProcess1D>& process,

                        Time end, Size steps, Real)

    : EqualProbabilitiesBinomialTree<AdditiveEQPBinomialTree>(process,

                                                              end, steps) {

        Real radicand = 4.0*process->variance(0.0, x0_, dt_)-

                        3.0*driftPerStep_*driftPerStep_;

        QL_REQUIRE(radicand >= 0.0,

                   "drift per step too large for the additive EQP tree: "

                   "more steps are needed");

        up_ = - 0.5 * driftPerStep_ + 0.5 * std::sqrt(radicand);

    }

    Trigeorgis::Trigeorgis(

                        const ext::shared_ptr<StochasticProcess1D>& process,

                        Time end, Size steps, Real)

    : EqualJumpsBinomialTree<Trigeorgis>(process, end, steps) {

        dx_ = std::sqrt(process->variance(0.0, x0_, dt_)+

                        driftPerStep_*driftPerStep_);

        pu_ = 0.5 + 0.5*driftPerStep_/dx_;;

        pd_ = 1.0 - pu_;

        QL_REQUIRE(pu_<=1.0, "negative probability");

        QL_REQUIRE(pu_>=0.0, "negative probability");

    }

    Tian::Tian(const ext::shared_ptr<StochasticProcess1D>& process,

               Time end, Size steps, Real)

    : BinomialTree<Tian>(process, end, steps) {

        Real q = std::exp(process->variance(0.0, x0_, dt_));

        Real r = std::exp(driftPerStep_)*std::sqrt(q);

        up_ = 0.5 * r * q * (q + 1 + std::sqrt(q * q + 2 * q - 3));

        down_ = 0.5 * r * q * (q + 1 - std::sqrt(q * q + 2 * q - 3));

        pu_ = (r - down_) / (up_ - down_);

        pd_ = 1.0 - pu_;

        // doesn't work

        //     treeCentering_ = (up_+down_)/2.0;

        //     up_ = up_-treeCentering_;

        QL_REQUIRE(pu_<=1.0, "negative probability");

        QL_REQUIRE(pu_>=0.0, "negative probability");

    }

    LeisenReimer::LeisenReimer(const ext::shared_ptr<StochasticProcess1D>& process,

                               Time end,

                               Size steps,

                               Real strike)

    : BinomialTree<LeisenReimer>(process, end, ((steps % 2) != 0U ? steps : (steps + 1))) {

        QL_REQUIRE(strike>0.0, "strike must be positive");

        Size oddSteps = ((steps % 2) != 0U ? steps : (steps + 1));

        Real variance = process->variance(0.0, x0_, end);

        Real ermqdt = std::exp(driftPerStep_ + 0.5*variance/oddSteps);

        Real d2 = (std::log(x0_/strike) + driftPerStep_*oddSteps ) /

                                                          std::sqrt(variance);

        const LeisenReimerStep step =

            leisenReimerStep(d2, ermqdt, variance, oddSteps);

        pu_ = step.upProbability;

        pd_ = step.downProbability;

        up_ = step.up;

        down_ = step.down;

    }

    Real Joshi4::computeUpProb(Real k, Real dj) const {

        Real alpha = dj/(std::sqrt(8.0));

        Real alpha2 = alpha*alpha;

        Real alpha3 = alpha*alpha2;

        Real alpha5 = alpha3*alpha2;

        Real alpha7 = alpha5*alpha2;

        Real beta = -0.375*alpha-alpha3;

        Real gamma = (5.0/6.0)*alpha5 + (13.0/12.0)*alpha3

            +(25.0/128.0)*alpha;

        Real delta = -0.1025 *alpha- 0.9285 *alpha3

            -1.43 *alpha5 -0.5 *alpha7;

        Real p =0.5;

        Real rootk = std::sqrt(k);

        p+= alpha/rootk;

        p+= beta /(k*rootk);

        p+= gamma/(k*k*rootk);

        // delete next line to get results for j three tree

        p+= delta/(k*k*k*rootk);

        return p;

    }

    Joshi4::Joshi4(const ext::shared_ptr<StochasticProcess1D>& process,

                   Time end,

                   Size steps,

                   Real strike)

    : BinomialTree<Joshi4>(process, end, (steps % 2) != 0U ? steps : (steps + 1)) {

        QL_REQUIRE(strike>0.0, "strike must be positive");

        Size oddSteps = (steps % 2) != 0U ? steps : (steps + 1);

        Real variance = process->variance(0.0, x0_, end);

        Real ermqdt = std::exp(driftPerStep_ + 0.5*variance/oddSteps);

        Real d2 = (std::log(x0_/strike) + driftPerStep_*oddSteps ) /

                                                          std::sqrt(variance);

        pu_ = computeUpProb((oddSteps-1.0)/2.0,d2 );

        QL_REQUIRE(pu_ > 0.0 && pu_ < 1.0, "invalid up probability: " << pu_);

        pd_ = 1.0 - pu_;

        Real pdash = computeUpProb((oddSteps-1.0)/2.0,d2+std::sqrt(variance));

        up_ = ermqdt * pdash / pu_;

        down_ = (ermqdt - pu_ * up_) / (1.0 - pu_);

    }

}