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// $Id: polynomial.h 30036 2013-07-18 16:55:32Z maier $
//
// Copyright (C) 2000 - 2013 by the deal.II authors
//
// This file is part of the deal.II library.
//
// The deal.II library is free software; you can use it, redistribute
// it, and/or modify it under the terms of the GNU Lesser General
// Public License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// The full text of the license can be found in the file LICENSE at
// the top level of the deal.II distribution.
//
// ---------------------------------------------------------------------
#ifndef __deal2__polynomial_h
#define __deal2__polynomial_h
#include <deal.II/base/config.h>
#include <deal.II/base/exceptions.h>
#include <deal.II/base/subscriptor.h>
#include <deal.II/base/point.h>
#include <deal.II/base/std_cxx1x/shared_ptr.h>
#include <vector>
DEAL_II_NAMESPACE_OPEN
/**
* @addtogroup Polynomials
* @{
*/
/**
* A namespace in which classes relating to the description of 1d polynomial
* spaces are declared.
*/
namespace Polynomials
{
/**
* Base class for all 1D polynomials. A polynomial is represented in
* this class by its coefficients, which are set through the
* constructor or by derived classes. Evaluation of a polynomial
* happens through the Horner scheme which provides both numerical
* stability and a minimal number of numerical operations.
*
* @author Ralf Hartmann, Guido Kanschat, 2000, 2006
*/
template <typename number>
class Polynomial : public Subscriptor
{
public:
/**
* Constructor. The coefficients of the polynomial are passed as
* arguments, and denote the polynomial $\sum_i a[i] x^i$, i.e. the first
* element of the array denotes the constant term, the second the linear
* one, and so on. The degree of the polynomial represented by this object
* is thus the number of elements in the <tt>coefficient</tt> array minus
* one.
*/
Polynomial (const std::vector<number> &coefficients);
/**
* Constructor creating a zero polynomial of degree @p n.
*/
Polynomial (const unsigned int n);
/**
* Constructor for Lagrange polynomial and its point of evaluation. The
* idea is to construct $\prod_{i\neq j} \frac{x-x_i}{x_j-x_i}$, where j
* is the evaluation point specified as argument and the support points
* contain all points (including x_j, which will internally not be
* stored).
*/
Polynomial (const std::vector<Point<1> > &lagrange_support_points,
const unsigned int evaluation_point);
/**
* Default constructor creating an illegal object.
*/
Polynomial ();
/**
* Return the value of this polynomial at the given point.
*
* This function uses the Horner scheme for numerical stability of the
* evaluation.
*/
number value (const number x) const;
/**
* Return the values and the derivatives of the Polynomial at point
* <tt>x</tt>. <tt>values[i], i=0,...,values.size()-1</tt> includes the
* <tt>i</tt>th derivative. The number of derivatives to be computed is
* thus determined by the size of the array passed.
*
* This function uses the Horner scheme for numerical stability of the
* evaluation.
*/
void value (const number x,
std::vector<number> &values) const;
/**
* Degree of the polynomial. This is the degree reflected by the number of
* coefficients provided by the constructor. Leading non-zero coefficients
* are not treated separately.
*/
unsigned int degree () const;
/**
* Scale the abscissa of the polynomial. Given the polynomial <i>p(t)</i>
* and the scaling <i>t = ax</i>, then the result of this operation is the
* polynomial <i>q</i>, such that <i>q(x) = p(t)</i>.
*
* The operation is performed in place.
*/
void scale (const number factor);
/**
* Shift the abscissa oft the polynomial. Given the polynomial
* <i>p(t)</i> and the shift <i>t = x + a</i>, then the result of this
* operation is the polynomial <i>q</i>, such that <i>q(x) = p(t)</i>.
*
* The template parameter allows to compute the new coefficients with
* higher accuracy, since all computations are performed with type
* <tt>number2</tt>. This may be necessary, since this operation involves
* a big number of additions. On a Sun Sparc Ultra with Solaris 2.8, the
* difference between <tt>double</tt> and <tt>long double</tt> was not
* significant, though.
*
* The operation is performed in place, i.e. the coefficients of the
* present object are changed.
*/
template <typename number2>
void shift (const number2 offset);
/**
* Compute the derivative of a polynomial.
*/
Polynomial<number> derivative () const;
/**
* Compute the primitive of a polynomial. the coefficient of the zero
* order term of the polynomial is zero.
*/
Polynomial<number> primitive () const;
/**
* Multiply with a scalar.
*/
Polynomial<number> &operator *= (const double s);
/**
* Multiply with another polynomial.
*/
Polynomial<number> &operator *= (const Polynomial<number> &p);
/**
* Add a second polynomial.
*/
Polynomial<number> &operator += (const Polynomial<number> &p);
/**
* Subtract a second polynomial.
*/
Polynomial<number> &operator -= (const Polynomial<number> &p);
/**
* Test for equality of two polynomials.
*/
bool operator == (const Polynomial<number> &p) const;
/**
* Print coefficients.
*/
void print(std::ostream &out) const;
/**
* Write or read the data of this object to or from a stream for the
* purpose of serialization.
*/
template <class Archive>
void serialize (Archive &ar, const unsigned int version);
protected:
/**
* This function performs the actual scaling.
*/
static void scale (std::vector<number> &coefficients,
const number factor);
/**
* This function performs the actual shift
*/
template <typename number2>
static void shift (std::vector<number> &coefficients,
const number2 shift);
/**
* Multiply polynomial by a factor.
*/
static void multiply (std::vector<number> &coefficients,
const number factor);
/**
* Transforms polynomial form of product of linear factors into standard
* form, $\sum_i a_i x^i$. Deletes all data structures related to the
* product form.
*/
void transform_into_standard_form ();
/**
* Coefficients of the polynomial $\sum_i a_i x^i$. This vector is filled
* by the constructor of this class and may be passed down by derived
* classes.
*
* This vector cannot be constant since we want to allow copying of
* polynomials.
*/
std::vector<number> coefficients;
/**
* Stores whether the polynomial is in Lagrange product form, i.e.,
* constructed as a product $(x-x_0) (x-x_1) \ldots (x-x_n)/c$, or not.
*/
bool in_lagrange_product_form;
/**
* If the polynomial is in Lagrange product form, i.e., constructed as a
* product $(x-x_0) (x-x_1) \ldots (x-x_n)/c$, store the shifts $x_i$.
*/
std::vector<number> lagrange_support_points;
/**
* If the polynomial is in Lagrange product form, i.e., constructed as a
* product $(x-x_0) (x-x_1) \ldots (x-x_n)/c$, store the weight c.
*/
number lagrange_weight;
};
/**
* Class generates Polynomial objects representing a monomial of
* degree n, that is, the function $x^n$.
*
* @author Guido Kanschat, 2004
*/
template <typename number>
class Monomial : public Polynomial<number>
{
public:
/**
* Constructor, taking the
* degree of the monomial and
* an optional coefficient as
* arguments.
*/
Monomial(const unsigned int n,
const double coefficient = 1.);
/**
* Return a vector of Monomial
* objects of degree zero
* through <tt>degree</tt>, which
* then spans the full space of
* polynomials up to the given
* degree. This function may be
* used to initialize the
* TensorProductPolynomials
* and PolynomialSpace
* classes.
*/
static
std::vector<Polynomial<number> >
generate_complete_basis (const unsigned int degree);
private:
/**
* Needed by constructor.
*/
static std::vector<number> make_vector(unsigned int n,
const double coefficient);
};
/**
* Lagrange polynomials with equidistant interpolation points in
* [0,1]. The polynomial of degree <tt>n</tt> has got <tt>n+1</tt> interpolation
* points. The interpolation points are sorted in ascending
* order. This order gives an index to each interpolation point. A
* Lagrangian polynomial equals to 1 at its `support point', and 0 at
* all other interpolation points. For example, if the degree is 3,
* and the support point is 1, then the polynomial represented by this
* object is cubic and its value is 1 at the point <tt>x=1/3</tt>, and zero
* at the point <tt>x=0</tt>, <tt>x=2/3</tt>, and <tt>x=1</tt>. All the polynomials
* have polynomial degree equal to <tt>degree</tt>, but together they span
* the entire space of polynomials of degree less than or equal
* <tt>degree</tt>.
*
* The Lagrange polynomials are implemented up to degree 10.
*
* @author Ralf Hartmann, 2000
*/
class LagrangeEquidistant: public Polynomial<double>
{
public:
/**
* Constructor. Takes the degree <tt>n</tt> of the Lagrangian polynom and
* the index <tt>support_point</tt> of the support point. Fills the
* <tt>coefficients</tt> of the base class Polynomial.
*/
LagrangeEquidistant (const unsigned int n,
const unsigned int support_point);
/**
* Return a vector of polynomial objects of degree <tt>degree</tt>, which
* then spans the full space of polynomials up to the given degree. The
* polynomials are generated by calling the constructor of this class with
* the same degree but support point running from zero to
* <tt>degree</tt>. This function may be used to initialize the
* TensorProductPolynomials and PolynomialSpace classes.
*/
static
std::vector<Polynomial<double> >
generate_complete_basis (const unsigned int degree);
private:
/**
* Computes the <tt>coefficients</tt> of the base class Polynomial. This
* function is <tt>static</tt> to allow to be called in the constructor.
*/
static
void
compute_coefficients (const unsigned int n,
const unsigned int support_point,
std::vector<double> &a);
};
/**
* Given a set of points along the real axis, this function returns all
* Lagrange polynomials for interpolation of these points. The number of
* polynomials is equal to the number of points and the maximum degree is
* one less.
*/
std::vector<Polynomial<double> >
generate_complete_Lagrange_basis (const std::vector<Point<1> > &points);
/**
* Legendre polynomials of arbitrary degree.
* Constructing a Legendre polynomial of degree <tt>p</tt>, the coefficients
* will be computed by the three-term recursion formula.
*
* @note The polynomials defined by this class differ in two aspects by what
* is usually referred to as Legendre polynomials: (i) This classes defines
* them on the reference interval $[0,1]$, rather than the commonly used
* interval $[-1,1]$. (ii) The polynomials have been scaled in such a way that
* they are orthonormal, not just orthogonal; consequently, the polynomials do
* not necessarily have boundary values equal to one.
*
* @author Guido Kanschat, 2000
*/
class Legendre : public Polynomial<double>
{
public:
/**
* Constructor for polynomial of
* degree <tt>p</tt>.
*/
Legendre (const unsigned int p);
/**
* Return a vector of Legendre
* polynomial objects of degrees
* zero through <tt>degree</tt>, which
* then spans the full space of
* polynomials up to the given
* degree. This function may be
* used to initialize the
* TensorProductPolynomials
* and PolynomialSpace
* classes.
*/
static
std::vector<Polynomial<double> >
generate_complete_basis (const unsigned int degree);
private:
/**
* Coefficients for the interval $[0,1]$.
*/
static std::vector<std_cxx1x::shared_ptr<const std::vector<double> > > shifted_coefficients;
/**
* Vector with already computed
* coefficients. For each degree of the
* polynomial, we keep one pointer to
* the list of coefficients; we do so
* rather than keeping a vector of
* vectors in order to simplify
* programming multithread-safe. In
* order to avoid memory leak, we use a
* shared_ptr in order to correctly
* free the memory of the vectors when
* the global destructor is called.
*/
static std::vector<std_cxx1x::shared_ptr<const std::vector<double> > > recursive_coefficients;
/**
* Compute coefficients recursively.
* The coefficients are stored in a
* static data vector to be available
* when needed next time. Since the
* recursion is performed for the
* interval $[-1,1]$, the polynomials
* are shifted to $[0,1]$ by the
* <tt>scale</tt> and <tt>shift</tt>
* functions of <tt>Polynomial</tt>,
* afterwards.
*/
static void compute_coefficients (const unsigned int p);
/**
* Get coefficients for
* constructor. This way, it can
* use the non-standard
* constructor of
* Polynomial.
*/
static const std::vector<double> &
get_coefficients (const unsigned int k);
};
/**
* Lobatto polynomials of arbitrary degree on <tt>[0,1]</tt>.
*
* These polynomials are the integrated Legendre polynomials on [0,1]. The
* first two polynomials are the standard linear shape functions given by
* $l_0(x) = 1-x$ and $l_1(x) = x$. For $i\geq2$ we use the definition $l_i(x)
* = \frac{1}{\Vert L_{i-1}\Vert_2}\int_0^x L_{i-1}(t)\,dt$, where $L_i$
* denotes the $i$-th Legendre polynomial on $[0,1]$. The Lobatto polynomials
* $l_0,\ldots,l_k$ form a complete basis of the polynomials space of degree
* $k$.
*
* Calling the constructor with a given index <tt>k</tt> will generate the
* polynomial with index <tt>k</tt>. But only for $k\geq 1$ the index equals
* the degree of the polynomial. For <tt>k==0</tt> also a polynomial of degree
* 1 is generated.
*
* These polynomials are used for the construction of the shape functions of
* Nédélec elements of arbitrary order.
*
* @author Markus Bürg, 2009
*/
class Lobatto : public Polynomial<double>
{
public:
/**
* Constructor for polynomial of degree
* <tt>p</tt>. There is an exception
* for <tt>p==0</tt>, see the general
* documentation.
*/
Lobatto (const unsigned int p = 0);
/**
* Return the polynomials with index
* <tt>0</tt> up to
* <tt>degree</tt>. There is an
* exception for <tt>p==0</tt>, see the
* general documentation.
*/
static std::vector<Polynomial<double> >
generate_complete_basis (const unsigned int p);
private:
/**
* Compute coefficients recursively.
*/
std::vector<double> compute_coefficients (const unsigned int p);
};
/**
* Hierarchical polynomials of arbitrary degree on <tt>[0,1]</tt>.
*
* When Constructing a Hierarchical polynomial of degree <tt>p</tt>,
* the coefficients will be computed by a recursion formula. The
* coefficients are stored in a static data vector to be available
* when needed next time.
*
* These hierarchical polynomials are based on those of Demkowicz, Oden,
* Rachowicz, and Hardy (CMAME 77 (1989) 79-112, Sec. 4). The first two
* polynomials are the standard linear shape functions given by
* $\phi_{0}(x) = 1 - x$ and $\phi_{1}(x) = x$. For $l \geq 2$
* we use the definitions $\phi_{l}(x) = (2x-1)^l - 1, l = 2,4,6,...$
* and $\phi_{l}(x) = (2x-1)^l - (2x-1), l = 3,5,7,...$. These satisfy the
* recursion relations $\phi_{l}(x) = (2x-1)\phi_{l-1}, l=3,5,7,...$ and
* $\phi_{l}(x) = (2x-1)\phi_{l-1} + \phi_{2}, l=4,6,8,...$.
*
* The degrees of freedom are the values at the vertices and the
* derivatives at the midpoint. Currently, we do not scale the
* polynomials in any way, although better conditioning of the
* element stiffness matrix could possibly be achieved with scaling.
*
* Calling the constructor with a given index <tt>p</tt> will generate the
* following: if <tt>p==0</tt>, then the resulting polynomial is the linear
* function associated with the left vertex, if <tt>p==1</tt> the one
* associated with the right vertex. For higher values of <tt>p</tt>, you
* get the polynomial of degree <tt>p</tt> that is orthogonal to all
* previous ones. Note that for <tt>p==0</tt> you therefore do <b>not</b>
* get a polynomial of degree zero, but one of degree one. This is to
* allow generating a complete basis for polynomial spaces, by just
* iterating over the indices given to the constructor.
*
* On the other hand, the function generate_complete_basis() creates
* a complete basis of given degree. In order to be consistent with
* the concept of a polynomial degree, if the given argument is zero,
* it does <b>not</b> return the linear polynomial described above, but
* rather a constant polynomial.
*
* @author Brian Carnes, 2002
*/
class Hierarchical : public Polynomial<double>
{
public:
/**
* Constructor for polynomial of
* degree <tt>p</tt>. There is an
* exception for <tt>p==0</tt>, see
* the general documentation.
*/
Hierarchical (const unsigned int p);
/**
* Return a vector of
* Hierarchical polynomial
* objects of degrees zero through
* <tt>degree</tt>, which then spans
* the full space of polynomials
* up to the given degree. Note
* that there is an exception if
* the given <tt>degree</tt> equals
* zero, see the general
* documentation of this class.
*
* This function may be
* used to initialize the
* TensorProductPolynomials,
* AnisotropicPolynomials,
* and PolynomialSpace
* classes.
*/
static
std::vector<Polynomial<double> >
generate_complete_basis (const unsigned int degree);
private:
/**
* Compute coefficients recursively.
*/
static void compute_coefficients (const unsigned int p);
/**
* Get coefficients for
* constructor. This way, it can
* use the non-standard
* constructor of
* Polynomial.
*/
static const std::vector<double> &
get_coefficients (const unsigned int p);
/**
* Vector with already computed
* coefficients. For each degree of the
* polynomial, we keep one pointer to
* the list of coefficients; we do so
* rather than keeping a vector of
* vectors in order to simplify
* programming multithread-safe. In
* order to avoid memory leak, we use a
* shared_ptr in order to correctly
* free the memory of the vectors when
* the global destructor is called.
*/
static std::vector<std_cxx1x::shared_ptr<const std::vector<double> > > recursive_coefficients;
};
/**
* Polynomials for Hermite interpolation condition.
*
* This is the set of polynomials of degree at least three, such that
* the following interpolation conditions are met: the polynomials and
* their first derivatives vanish at the values <i>x</i>=0 and
* <i>x</i>=1, with the exceptions <i>p</i><sub>0</sub>(0)=1,
* <i>p</i><sub><i>1</i></sub>(1)=1, <i>p</i>'<sub>2</sub>(0)=1,
* <i>p'</i><sub>3</sub>(1)=1.
*
* For degree three, we obtain the standard four Hermitian
* interpolation polynomials, see for instance <a
* href="http://en.wikipedia.org/wiki/Cubic_Hermite_spline">Wikipedia</a>.
* For higher degrees, these are augmented
* first, by the polynomial of degree four with vanishing values and
* derivatives at <i>x</i>=0 and <i>x</i>=1, then by the product of
* this fourth order polynomial with Legendre polynomials of
* increasing order. The implementation is
* @f{align*}{
* p_0(x) &= 2x^3-3x^2+1 \\
* p_1(x) &= -2x^2+3x^2 \\
* p_2(x) &= x^3-2x^2+x \\
* p_3(x) &= x^3-x^2 \\
* p_4(x) &= 16x^2(x-1)^2 \\
* \ldots & \ldots \\
* p_k(x) &= x^2(x-1)^2 L_{k-4}(x)
* @f}
*
* @author Guido Kanschat
* @date 2012
*/
class HermiteInterpolation : public Polynomial<double>
{
public:
/**
* Constructor for polynomial
* with index <tt>p</tt>. See
* the class documentation on
* the definition of the
* sequence of polynomials.
*/
HermiteInterpolation (const unsigned int p);
/**
* Return the polynomials with index
* <tt>0</tt> up to
* <tt>p+1</tt> in a space of
* degree up to
* <tt>p</tt>. Here, <tt>p</tt>
* has to be at least 3.
*/
static std::vector<Polynomial<double> >
generate_complete_basis (const unsigned int p);
};
}
/** @} */
/* -------------------------- inline functions --------------------- */
namespace Polynomials
{
template <typename number>
inline
Polynomial<number>::Polynomial ()
:
in_lagrange_product_form (false),
lagrange_weight (1.)
{}
template <typename number>
inline
unsigned int
Polynomial<number>::degree () const
{
if (in_lagrange_product_form == true)
{
return lagrange_support_points.size();
}
else
{
Assert (coefficients.size()>0, ExcEmptyObject());
return coefficients.size() - 1;
}
}
template <typename number>
inline
number
Polynomial<number>::value (const number x) const
{
if (in_lagrange_product_form == false)
{
Assert (coefficients.size() > 0, ExcEmptyObject());
// Horner scheme
const unsigned int m=coefficients.size();
number value = coefficients.back();
for (int k=m-2; k>=0; --k)
value = value*x + coefficients[k];
return value;
}
else
{
// direct evaluation of Lagrange polynomial
const unsigned int m = lagrange_support_points.size();
number value = 1.;
for (unsigned int j=0; j<m; ++j)
value *= x-lagrange_support_points[j];
value *= lagrange_weight;
return value;
}
}
template <typename number>
template <class Archive>
inline
void
Polynomial<number>::serialize (Archive &ar, const unsigned int)
{
// forward to serialization function in the base class.
ar &static_cast<Subscriptor &>(*this);
ar &coefficients;
ar &in_lagrange_product_form;
ar &lagrange_support_points;
ar &lagrange_weight;
}
}
DEAL_II_NAMESPACE_CLOSE
#endif
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