/usr/include/CGAL/Polynomial/polynomial_gcd.h is in libcgal-dev 4.7-4.
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// All rights reserved.
//
// This file is part of CGAL (www.cgal.org); you can 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 3 of the License,
// or (at your option) any later version.
//
// Licensees holding a valid commercial license may use this file in
// accordance with the commercial license agreement provided with the software.
//
// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
//
// $URL$
// $Id$
//
//
// Author(s) : Arno Eigenwillig <arno@mpi-inf.mpg.de>
// Tobias Reithmann <treith@mpi-inf.mpg.de>
// Michael Hemmer <hemmer@informatik.uni-mainz.de>
// Michael Kerber <mkerber@mpi-inf.mpg.de>
// Dominik Huelse <dominik.huelse@gmx.de>
// ============================================================================
/*! \file CGAL/Polynomial/polynomial_gcd.h
* \brief Greatest common divisors and related operations on polynomials.
*/
#ifndef CGAL_POLYNOMIAL_GCD_H
#define CGAL_POLYNOMIAL_GCD_H
#include <CGAL/config.h>
#ifndef CGAL_USE_INTERNAL_MODULAR_GCD
#define CGAL_USE_INTERNAL_MODULAR_GCD 1
#endif
#include <CGAL/basic.h>
#include <CGAL/Residue.h>
#include <CGAL/Polynomial.h>
#include <CGAL/Scalar_factor_traits.h>
#include <CGAL/Real_timer.h>
#include <CGAL/Polynomial/Polynomial_type.h>
#include <CGAL/Polynomial/misc.h>
#include <CGAL/Polynomial/polynomial_gcd_implementations.h>
#include <CGAL/polynomial_utils.h>
#ifdef CGAL_USE_NTL
#include <CGAL/Polynomial/polynomial_gcd_ntl.h>
#endif
#if CGAL_USE_INTERNAL_MODULAR_GCD
#include <CGAL/Polynomial/modular_gcd.h>
#endif
// 1) gcd (basic form without cofactors)
// uses three level of dispatch on tag types:
// a) if the algebra type of the innermost coefficient is a field,
// ask for decomposability. for UFDs compute the gcd directly
// b) if NT supports integralization, the gcd is computed on
// integralized polynomials
// c) over a field (unless integralized), use the Euclidean algorithm;
// over a UFD, use the subresultant algorithm
//
// NOTICE: For better performance, especially in AlciX, there exist special
// modular implementations for the polynmials with coefficient type
// leda::integer and the CORE::BigInt type which use, when the
// NTL library is available.
// see CGAL/Polynomial/polynomial_gcd_ntl.h
namespace CGAL {
namespace internal {
template <class NT>
inline
Polynomial<NT> gcd_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
Field_tag)
{
return CGAL::internal::gcd_utcf_(p1,p2);
}
template <class NT>
inline
Polynomial<NT> gcd_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
Unique_factorization_domain_tag)
{
typedef Polynomial<NT> POLY;
typedef Polynomial_traits_d<POLY> PT;
typedef typename PT::Innermost_coefficient_type IC;
typename PT::Multivariate_content mcont;
IC mcont_p1 = mcont(p1);
IC mcont_p2 = mcont(p2);
typename CGAL::Coercion_traits<POLY,IC>::Cast ictp;
POLY p1_ = CGAL::integral_division(p1,ictp(mcont_p1));
POLY p2_ = CGAL::integral_division(p2,ictp(mcont_p2));
return CGAL::internal::gcd_utcf_(p1_, p2_) * ictp(CGAL::gcd(mcont_p1, mcont_p2));
}
// name gcd() forwarded to the internal::gcd_() dispatch function
/*! \ingroup CGAL_Polynomial
* \relates CGAL::Polynomial
* \brief return the greatest common divisor of \c p1 and \c p2
*
* \pre Requires \c Innermost_coefficient_type to be a \c Field or a \c UFDomain.
*/
template <class NT>
inline
Polynomial<NT> gcd_(const Polynomial<NT>& p1, const Polynomial<NT>& p2)
{
typedef typename internal::Innermost_coefficient_type<Polynomial<NT> >::Type IC;
typedef typename Algebraic_structure_traits<IC>::Algebraic_category Algebraic_category;
// Filter for zero-polynomials
if( p1 == Polynomial<NT>(0) )
return p2;
if( p2 == Polynomial<NT>(0) )
return p1;
return internal::gcd_(p1,p2,Algebraic_category());
}
} // namespace internal
// 2) gcd_utcf computation
// (gcd up to scalar factors, for non-UFD non-field coefficients)
// a) first try to decompose the coefficients
// b) second dispatch depends on the algebra type of NT
namespace internal {
template <class NT> Polynomial<NT> inline
gcd_utcf_(const Polynomial<NT>& p1, const Polynomial<NT>& p2){
typedef CGAL::Fraction_traits< Polynomial<NT> > FT;
typedef typename FT::Is_fraction Is_fraction;
return gcd_utcf_is_fraction_(p1, p2, Is_fraction());
}
// is fraction ?
template <class NT> Polynomial<NT> inline
gcd_utcf_is_fraction_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_true)
{
typedef Polynomial<NT> POLY;
typedef Polynomial_traits_d<POLY> PT;
typedef Fraction_traits<POLY> FT;
typename FT::Denominator_type dummy;
typename FT::Numerator_type p1i, p2i;
typename FT::Decompose()(p1,p1i, dummy);
typename FT::Decompose()(p2,p2i, dummy);
typename Coercion_traits<POLY,typename FT::Numerator_type>::Cast cast;
return typename PT::Canonicalize()(cast(internal::gcd_utcf_(p1i, p2i)));
}
template <class NT> Polynomial<NT> inline
gcd_utcf_is_fraction_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_false)
{
typedef Algebraic_structure_traits< Polynomial<NT> > NTT;
typedef CGAL::Modular_traits<Polynomial<NT> > MT;
return gcd_utcf_modularizable_algebra_(
p1,p2,typename MT::Is_modularizable(),typename NTT::Algebraic_category());
}
// is type modularizable
template <class NT> Polynomial<NT> inline
gcd_utcf_modularizable_algebra_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_false,
Integral_domain_tag){
return internal::gcd_utcf_Integral_domain(p1, p2);
}
template <class NT> Polynomial<NT> inline
gcd_utcf_modularizable_algebra_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_false,
Unique_factorization_domain_tag){
return internal::gcd_utcf_UFD(p1, p2);
}
template <class NT> Polynomial<NT> inline
gcd_utcf_modularizable_algebra_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_false,
Euclidean_ring_tag){
return internal::gcd_Euclidean_ring(p1, p2);
}
#if CGAL_USE_INTERNAL_MODULAR_GCD
template <class NT> Polynomial<NT> inline
gcd_utcf_modularizable_algebra_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_true,
Integral_domain_tag tag){
return modular_gcd_utcf(p1, p2, tag);
}
template <class NT> Polynomial<NT> inline
gcd_utcf_modularizable_algebra_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_true,
Unique_factorization_domain_tag tag){
return modular_gcd_utcf(p1, p2, tag);
// return modular_gcd_utcf_algorithm_M(p1, p2);
}
#else
template <class NT> Polynomial<NT> inline
gcd_utcf_modularizable_algebra_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_true,
Integral_domain_tag){
return internal::gcd_utcf_Integral_domain(p1, p2);
}
template <class NT> Polynomial<NT> inline
gcd_utcf_modularizable_algebra_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_true,
Unique_factorization_domain_tag){
return internal::gcd_utcf_UFD(p1, p2);
}
#endif
template <class NT> Polynomial<NT> inline
gcd_utcf_modularizable_algebra_(
const Polynomial<NT>& p1,
const Polynomial<NT>& p2,
::CGAL::Tag_true,
Euclidean_ring_tag){
// No modular algorithm available
return internal::gcd_Euclidean_ring(p1, p2);
}
template <class NT> Polynomial<NT> inline
gcd_utcf(const Polynomial<NT>& p1, const Polynomial<NT>& p2){
return internal::gcd_utcf_(p1,p2);
}
} // namespace internal
// 3) extended gcd computation (with cofactors)
// with dispatch similar to gcd
namespace internal {
template <class NT>
inline
Polynomial<NT> gcdex_(
Polynomial<NT> x, Polynomial<NT> y,
Polynomial<NT>& xf, Polynomial<NT>& yf,
::CGAL::Tag_false
) {
typedef typename Algebraic_structure_traits<NT>::Algebraic_category Algebraic_category;
return gcdex_(x, y, xf, yf, Algebraic_category());
}
template <class NT>
inline
Polynomial<NT> gcdex_(
Polynomial<NT> x, Polynomial<NT> y,
Polynomial<NT>& xf, Polynomial<NT>& yf,
Field_tag
) {
/* The extended Euclidean algorithm for univariate polynomials.
* See [Cohen, 1993], algorithm 3.2.2
*/
typedef Polynomial<NT> POLY;
typename Algebraic_structure_traits<NT>::Integral_div idiv;
// handle trivial cases
if (x.is_zero()) {
if (y.is_zero()) CGAL_error_msg("gcdex(0,0) is undefined");
xf = NT(0); yf = idiv(NT(1), y.unit_part());
return yf * y;
}
if (y.is_zero()) {
yf = NT(0); xf = idiv(NT(1), x.unit_part());
return xf * x;
}
bool swapped = x.degree() < y.degree();
if (swapped) { POLY t = x; x = y; y = t; }
// main loop
POLY u = x, v = y, q, r, m11(1), m21(0), m21old;
for (;;) {
/* invariant: (i) There exist m12 and m22 such that
* u = m11*x + m12*y
* v = m21*x + m22*y
* (ii) and we have
* gcd(u,v) == gcd(x,y)
*/
// compute next element of remainder sequence
POLY::euclidean_division(u, v, q, r); // u == qv + r
if (r.is_zero()) break;
// update u and v while preserving invariant
u = v; v = r;
/* Since r = u - qv, this preserves invariant (part ii)
* and corresponds to the matrix assignment
* (u) = (0 1) (u)
* (v) (1 -q) (v)
*/
m21old = m21; m21 = m11 - q*m21; m11 = m21old;
/* This simulates the matching matrix assignment
* (m11 m12) = (0 1) (m11 m12)
* (m21 m22) (1 -q) (m21 m22)
* which preserves the invariant (part i)
*/
if (r.degree() == 0) break;
}
/* postcondition: invariant holds and v divides u */
// make gcd unit-normal
m21 /= v.unit_part(); v /= v.unit_part();
// obtain m22 such that v == m21*x + m22*y
POLY m22;
POLY::euclidean_division(v - m21*x, y, m22, r);
CGAL_assertion(r.is_zero());
// check computation
CGAL_assertion(v == m21*x + m22*y);
// return results
if (swapped) {
xf = m22; yf = m21;
} else {
xf = m21; yf = m22;
}
return v;
}
template <class NT>
inline
Polynomial<NT> gcdex_(
Polynomial<NT> x, Polynomial<NT> y,
Polynomial<NT>& xf, Polynomial<NT>& yf,
::CGAL::Tag_true
) {
typedef Polynomial<NT> POLY;
typedef typename CGAL::Fraction_traits<POLY>::Numerator_type INTPOLY;
typedef typename CGAL::Fraction_traits<POLY>::Denominator_type DENOM;
typedef typename INTPOLY::NT INTNT;
typename CGAL::Fraction_traits<POLY>::Decompose decompose;
typename CGAL::Fraction_traits<POLY>::Compose compose;
// rewrite x as xi/xd and y as yi/yd with integral polynomials xi, yi
DENOM xd, yd;
x.simplify_coefficients();
y.simplify_coefficients();
INTPOLY xi ,yi;
decompose(x,xi,xd);
decompose(y,yi,yd);
// compute the integral gcd with cofactors:
// vi = gcd(xi, yi); vfi*vi == xfi*xi + yfi*yi
INTPOLY xfi, yfi; INTNT vfi;
INTPOLY vi = pseudo_gcdex(xi, yi, xfi, yfi, vfi);
// proceed to vfi*v == xfi*x + yfi*y with v = gcd(x,y) (unit-normal)
POLY v = compose(vi, vi.lcoeff());
v.simplify_coefficients();
CGAL_assertion(v.unit_part() == NT(1));
vfi *= vi.lcoeff(); xfi *= xd; yfi *= yd;
// compute xf, yf such that gcd(x,y) == v == xf*x + yf*y
xf = compose(xfi, vfi);
yf = compose(yfi, vfi);
xf.simplify_coefficients();
yf.simplify_coefficients();
return v;
}
} // namespace internal
/*! \ingroup CGAL_Polynomial
* \relates CGAL::Polynomial
* \brief compute gcd with cofactors
*
* This function computes the gcd of polynomials \c p1 and \c p2
* along with two other polynomials \c f1 and \c f2 such that
* gcd(\e p1, \e p2) = <I>f1*p1 + f2*p2</I>. This is called
* <I>extended</I> gcd computation, and <I>f1, f2</I> are called
* <I>Bézout factors</I> or <I>cofactors</I>.
*
* CGALially, computation is performed ``denominator-free'' if
* supported by the coefficient type via \c CGAL::Fraction_traits
* (using \c pseudo_gcdex() ), otherwise the euclidean remainder
* sequence is used.
*
* \pre \c NT must be a \c Field.
*
* The result <I>d</I> is unit-normal,
* i.e. <I>d</I><TT>.lcoeff() == NT(1)</TT>.
*
*/
template <class NT>
inline
Polynomial<NT> gcdex(
Polynomial<NT> p1, Polynomial<NT> p2,
Polynomial<NT>& f1, Polynomial<NT>& f2
) {
typedef typename CGAL::Fraction_traits< Polynomial<NT> >
::Is_fraction Is_fraction;
return internal::gcdex_(p1, p2, f1, f2, Is_fraction());
}
/*! \ingroup CGAL_Polynomial
* \relates CGAL::Polynomial
* \brief compute gcd with ``almost'' cofactors
*
* This is a variant of \c exgcd() for use over non-field \c NT.
* It computes the gcd of polynomials \c p1 and \c p2
* along with two other polynomials \c f1 and \c f2 and a scalar \c v
* such that \e v * gcd(\e p1, \e p2) = <I>f1*p1 + f2*p2</I>,
* using the subresultant remainder sequence. That \c NT is not a field
* implies that one cannot achieve \e v = 1 for all inputs.
*
* \pre \c NT must be a \c UFDomain of scalars (not polynomials).
*
* The result is unit-normal.
*
*/
template <class NT>
inline
Polynomial<NT> pseudo_gcdex(
#ifdef DOXYGEN_RUNNING
Polynomial<NT> p1, Polynomial<NT> p2,
Polynomial<NT>& f2, Polynomial<NT>& f2, NT& v
#else
Polynomial<NT> x, Polynomial<NT> y,
Polynomial<NT>& xf, Polynomial<NT>& yf, NT& vf
#endif // DOXYGEN_RUNNING
) {
/* implemented using the extended subresultant algorithm
* for gcd computation with Bezout factors
*
* To understand this, you need to understand the computation of
* cofactors as in the basic extended Euclidean algorithm (see
* the code above of gcdex_(..., Field_tag)), and the subresultant
* gcd algorithm, see gcd_(..., Unique_factorization_domain_tag).
*
* The crucial point of the combination of both is the observation
* that the subresultant factor (called rho here) divided out of the
* new remainder in each step can also be divided out of the
* cofactors.
*/
typedef Polynomial<NT> POLY;
typename Algebraic_structure_traits<NT>::Integral_division idiv;
typename Algebraic_structure_traits<NT>::Gcd gcd;
// handle trivial cases
if (x.is_zero()) {
if (y.is_zero()) CGAL_error_msg("gcdex(0,0) is undefined");
xf = POLY(0); yf = POLY(1); vf = y.unit_part();
return y / vf;
}
if (y.is_zero()) {
xf = POLY(1); yf = POLY(0); vf = x.unit_part();
return x / vf;
}
bool swapped = x.degree() < y.degree();
if (swapped) { POLY t = x; x = y; y = t; }
// compute gcd of content
NT xcont = x.content(); NT ycont = y.content();
NT gcdcont = gcd(xcont, ycont);
// compute gcd of primitive parts
POLY xprim = x / xcont; POLY yprim = y / ycont;
POLY u = xprim, v = yprim, q, r;
POLY m11(1), m21(0), m21old;
NT g(1), h(1), d, rho;
for (;;) {
int delta = u.degree() - v.degree();
POLY::pseudo_division(u, v, q, r, d);
CGAL_assertion(d == ipower(v.lcoeff(), delta+1));
if (r.is_zero()) break;
rho = g * ipower(h, delta);
u = v; v = r / rho;
m21old = m21; m21 = (d*m11 - q*m21) / rho; m11 = m21old;
/* The transition from (u, v) to (v, r/rho) corresponds
* to multiplication with the matrix
* __1__ (0 rho)
* rho (d -q)
* The comments and correctness arguments from
* gcdex(..., Field_tag) apply analogously.
*/
g = u.lcoeff();
CGAL::internal::hgdelta_update(h, g, delta);
if (r.degree() == 0) break;
}
// obtain v == m21*xprim + m22*yprim
// the correct m21 was already computed above
POLY m22;
POLY::euclidean_division(v - m21*xprim, yprim, m22, r);
CGAL_assertion(r.is_zero());
// now obtain gcd(x,y) == gcdcont * v/v.content() == (m21*x + m22*y)/denom
NT vcont = v.content(), vup = v.unit_part();
v /= vup * vcont; v *= gcdcont;
m21 *= ycont; m22 *= xcont;
vf = idiv(xcont, gcdcont) * ycont * (vup * vcont);
CGAL_assertion(vf * v == m21*x + m22*y);
// return results
if (swapped) {
xf = m22; yf = m21;
} else {
xf = m21; yf = m22;
}
return v;
}
} // namespace CGAL
#endif // CGAL_POLYNOMIAL_GCD_H
// EOF
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