segmentintegral.hpp

/* -*- mode: c++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 
/*
 Copyright (C) 2000, 2001, 2002, 2003 RiskMap srl
 Copyright (C) 2015 Peter Caspers
 
 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.
*/
 
#ifndef quantlib_segment_integral_h
#define quantlib_segment_integral_h
 
#include <ql/math/integrals/integral.hpp>
#include <ql/math/comparison.hpp>
#include <ql/errors.hpp>
 
namespace QuantLib {
 
 
    class SegmentIntegral : public Integrator {
      public:
        explicit SegmentIntegral(Size intervals);
      protected:
        Real integrate(const ext::function<Real(Real)>& f, Real a, Real b) const override;
 
      private:
        Size intervals_;
    };
 
 
    // inline and template definitions
 
    inline Real
    SegmentIntegral::integrate(const ext::function<Real (Real)>& f,
                               Real a,
                               Real b) const {
        if(close_enough(a,b))
            return 0.0;
        Real dx = (b-a)/intervals_;
        Real sum = 0.5*(f(a)+f(b));
        Real end = b - 0.5*dx;
        for (Real x = a+dx; x < end; x += dx)
            sum += f(x);
        return sum*dx;
    }
 
}
 
#endif