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/* -*- mode: c++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */ /* Copyright (C) 2010 Kakhkhor Abdijalilov 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 <http://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. */ /*! \file zigguratrng.hpp \brief Ziggurat random-number generator */ #ifndef quantlib_ziggurat_generator_hpp #define quantlib_ziggurat_generator_hpp #include <ql/math/randomnumbers/mt19937uniformrng.hpp> #include <ql/math/randomnumbers/randomsequencegenerator.hpp> namespace QuantLib { //! Ziggurat random-number generator /*! This generator returns standard normal variates using the Ziggurat method. The underlying RNG is mt19937 (32 bit version). The algorithm is described in Marsaglia and Tsang (2000). "The Ziggurat Method for Generating Random Variables". Journal of Statistical Software 5 (8). Note that step 2 from the above paper reuses the rightmost 8 bits of the random integer, which creates correlation between steps 1 and 2. This implementation was written from scratch, following Marsaglia and Tsang. It avoids the correlation by using only the leftmost 24 bits of mt19937's output. Note that the GNU GSL implementation uses a different value for the right-most step. The GSL value is somewhat different from the one reported by Marsaglia and Tsang because GSL uses a different tail. This implementation uses the same right-most step as reported by Marsaglia and Tsang. The generator was put through Marsaglia's Diehard battery of tests and didn't exibit any abnormal behavior. */ 00052 class ZigguratRng { public: typedef Sample<Real> sample_type; ZigguratRng(unsigned long seed = 0); sample_type next() const { return sample_type(nextGaussian(),1.0); } private: mutable MersenneTwisterUniformRng mt32_; Real nextGaussian() const; }; // RNG traits for Ziggurat generator 00065 struct Ziggurat { // typedefs typedef ZigguratRng rng_type; typedef RandomSequenceGenerator<rng_type> rsg_type; // more traits enum { allowsErrorEstimate = 1 }; // factory static rsg_type make_sequence_generator(Size dimension, BigNatural seed) { return rsg_type(dimension, seed); } }; } #endif

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