QuantLib: a free/open-source library for quantitative finance
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bspline.hpp
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1/* -*- mode: c++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
2
3/*
4 Copyright (C) 2007 Allen Kuo
5
6 This file is part of QuantLib, a free-software/open-source library
7 for financial quantitative analysts and developers - http://quantlib.org/
8
9 QuantLib is free software: you can redistribute it and/or modify it
10 under the terms of the QuantLib license. You should have received a
11 copy of the license along with this program; if not, please email
12 <quantlib-dev@lists.sf.net>. The license is also available online at
13 <http://quantlib.org/license.shtml>.
14
15 This program is distributed in the hope that it will be useful, but WITHOUT
16 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
17 FOR A PARTICULAR PURPOSE. See the license for more details.
18*/
19
20/*! \file bspline.hpp
21 \brief B-spline basis functions
22*/
23
24#ifndef quantlib_bspline_hpp
25#define quantlib_bspline_hpp
26
27#include <ql/types.hpp>
28#include <vector>
29
30namespace QuantLib {
31
32 //! B-spline basis functions
33 /*! Follows treatment and notation from:
34
35 Weisstein, Eric W. "B-Spline." From MathWorld--A Wolfram Web
36 Resource. <http://mathworld.wolfram.com/B-Spline.html>
37
38 \f$ (p+1) \f$-th order B-spline (or p degree polynomial) basis
39 functions \f$ N_{i,p}(x), i = 0,1,2 \ldots n \f$, with \f$ n+1 \f$
40 control points, or equivalently, an associated knot vector
41 of size \f$ p+n+2 \f$ defined at the increasingly sorted points
42 \f$ (x_0, x_1 \ldots x_{n+p+1}) \f$. A linear B-spline has
43 \f$ p=1 \f$, quadratic B-spline has \f$ p=2 \f$, a cubic
44 B-spline has \f$ p=3 \f$, etc.
45
46 The B-spline basis functions are defined recursively
47 as follows:
48
49 \f[
50 \begin{array}{rcl}
51 N_{i,0}(x) &=& 1 \textrm{\ if\ } x_{i} \leq x < x_{i+1} \\
52 &=& 0 \textrm{\ otherwise} \\
53 N_{i,p}(x) &=& N_{i,p-1}(x) \frac{(x - x_{i})}{ (x_{i+p-1} - x_{i})} +
54 N_{i+1,p-1}(x) \frac{(x_{i+p} - x)}{(x_{i+p} - x_{i+1})}
55 \end{array}
56 \f]
57 */
58 class BSpline {
59 public:
61 Natural n,
62 const std::vector<Real>& knots);
63
64 Real operator()(Natural i, Real x) const;
65
66 private:
67 // recursive definition of N, the B-spline basis function
68 Real N(Natural i, Natural p, Real x) const;
69 // e.g. p_=2 is a quadratic B-spline, p_=3 is a cubic B-Spline, etc.
71 // n_ + 1 = "control points" = max number of basis functions
73 std::vector<Real> knots_;
74 };
75
76}
77
78
79#endif
B-spline basis functions.
Definition: bspline.hpp:58
Real N(Natural i, Natural p, Real x) const
Definition: bspline.cpp:49
std::vector< Real > knots_
Definition: bspline.hpp:73
Real operator()(Natural i, Real x) const
Definition: bspline.cpp:43
QL_REAL Real
real number
Definition: types.hpp:50
unsigned QL_INTEGER Natural
positive integer
Definition: types.hpp:43
Definition: any.hpp:35
Custom types.