#include <CGAL/Sqrt_extension.h>

Definition

template<typename NT, typename ROOT, typename DifferentExtensionComparable = Tag_false, typename FilterPredicates = Tag_false>
class CGAL::Sqrt_extension< NT, ROOT, DifferentExtensionComparable, FilterPredicates >

An instance of this class represents an extension of the type NT by one square root of the type ROOT.

NT is required to be constructible from ROOT.

NT is required to be an IntegralDomainWithoutDivision.

Sqrt_extension is RealEmbeddable if NT is RealEmbeddable.

For example, let Integer be some type representing \( \Z\), then Sqrt_extension<Integer,Integer> is able to represent \( \Z[\sqrt{\mathrm{root}}]\) for some arbitrary Integer \(\mathrm{root}\). \( R[a]\) denotes the extension of a ring \( R\) by an element \( a\). See also: http://mathworld.wolfram.com/ExtensionRing.html The value of \(\mathrm{root}\) is set at construction time, or set to zero if it is not specified.

Arithmetic operations among different extensions, say \( \Z[\sqrt{a}]\) and \( \Z[\sqrt{b}]\), are not supported. The result would be in \( \Z[\sqrt{a},\sqrt{b}]\), which is not representable by Sqrt_extension<Integer,Integer>.

Attention: The user is responsible to check that arithmetic operations are carried out for elements from the same extensions only.

This is not tested by Sqrt_extension for efficiency reasons. A violation of the precondition leads to undefined behavior. Be aware that for efficiency reasons the given \(\mathrm{root}\) is stored as it is given to the constructor. In particular, an extension by a square root of a square is considered as an extension.

Since elements of Sqrt_extension that lie in different extensions are not interoperable with respect to any arithmetic operations, the full value range of Sqrt_extension does not represent an algebraic structure. However, each subset of the value range that represents the extension of NT by a particular square root is a valid algebraic structure, since this subset is closed under all provided arithmetic operations. From there, Sqrt_extension can be used as if it were a model of an algebraic structure concept, with the following correspondence:

NT	`Sqrt_extension`


`IntegralDomainWithoutDivision`	`IntegralDomainWithoutDivision`
`IntegralDomain`	`IntegralDomain`
`UniqueFactorizationDomain`	`IntegralDomain`
`EuclideanRing`	`IntegralDomain`
`Field`	`Field`

The extension of a UniqueFactorizationDomain or EuclideanRing is just an IntegralDomain, since the extension in general destroys the unique factorization property. For instance consider \( \Z[\sqrt{10}]\), the extension of \( \Z\) by \( \sqrt{10}\): in \( \Z[\sqrt{10}]\) the element 10 has two different factorizations \( \sqrt{10} \cdot \sqrt{10}\) and \( 2 \cdot 5\). In particular, the factorization is not unique.

If NT is a model of RealEmbeddable the type Sqrt_extension is also considered as RealEmbeddable. However, by default it is not allowed to compare values from different extensions for efficiency reasons. In case such a comparison becomes necessary, use the member function compare with the according Boolean flag. If such a comparison is a very frequent case, override the default of DifferentExtensionComparable by giving CGAL::Tag_true as third template parameter. This effects the behavior of compare functions as well as the compare operators.

The fourth template argument, FilterPredicates, triggers an internal filter that may speed up comparisons and sign computations. In case FilterPredicates is set to CGAL::Tag_true the type first computes a double interval containing the represented number and tries to perform the comparison or sign computation using this interval. Once computed, this interval is stored by the corresponding Sqrt_extension object for further usage. Note that this internal filter is switched off by default, since it may conflict with other filtering methods, such as Lazy_exact_nt<Sqrt_extension>.

In case NT is not RealEmbeddable, DifferentExtensionComparable as well as FilterPredicates have no effect.

Is Model Of:

Assignable

CopyConstructible

DefaultConstructible

EqualityComparable

ImplicitInteroperable with int

ImplicitInteroperable with NT

Fraction if NT is a Fraction

RootOf_2

See Also: IntegralDomainWithoutDivision; IntegralDomain; Field; RealEmbeddable; CGAL::Tag_true; CGAL::Tag_false

Related Functions
(Note that these are not member functions.)
Sqrt_extension	operator+ (const Sqrt_extension &a, const Sqrt_extension &b)

Sqrt_extension	operator- (const Sqrt_extension &a, const Sqrt_extension &b)

Sqrt_extension	operator* (const Sqrt_extension &a, const Sqrt_extension &b)

Sqrt_extension	operator/ (const Sqrt_extension &a, const Sqrt_extension &b)

bool	operator== (const Sqrt_extension &a, const Sqrt_extension &b)

bool	operator!= (const Sqrt_extension &a, const Sqrt_extension &b)

bool	operator< (const Sqrt_extension &a, const Sqrt_extension &b)

bool	operator<= (const Sqrt_extension &a, const Sqrt_extension &b)

bool	operator> (const Sqrt_extension &a, const Sqrt_extension &b)

bool	operator>= (const Sqrt_extension &a, const Sqrt_extension &b)

std::ostream &	operator<< (std::ostream &os, const Sqrt_extension< NT, ROOT > &ext)
	writes `ext` to ostream `os`. More...

std::istream &	operator>> (std::istream &is, const Sqrt_extension< NT, ROOT > &ext)
	reads `ext` from istream `is` in format `EXT[a0,a1,root]`, the output format in mode `CGAL::IO::ASCII` More...

Creation
	Sqrt_extension ()
	Introduces a variable `ext` initialized with 0.

	Sqrt_extension (const Sqrt_extension &x)
	Copy constructor.

	Sqrt_extension (const int &i)
	Introduces a variable `ext` initialized with \( i\).

	Sqrt_extension (const NT &x)
	Introduces a variable `ext` initialized with \( x\).

	Sqrt_extension (int a0, int a1, int r)
	Constructor from int: `ext` \( = a0 +a1 \cdot sqrt(r)\). More...

	Sqrt_extension (NT a0, NT a1, ROOT r)
	General constructor: `ext` \( = a0 + a1 \cdot sqrt(r)\). More...

Operations
An object of type `Sqrt_extension` represent an expression of the form: \( a0 + a1 \sqrt(\mathrm{root}) \).
const NT &	a0 () const
	Const access operator for a0.

const NT &	a1 () const
	Const access operator for a1.

const ROOT &	root () const
	Const access operator for root.

bool	is_extended () const
	Returns true in case root of `ext` is not zero. More...

void	simplify ()
	Simplifies the representation, in particular \(\mathrm{root}\) is set to zero if \( a1\) is zero, that is, `ext` becomes not extended. More...

bool	is_zero () const
	returns true if `ext` represents the value zero.

CGAL::Sign	sign () const
	Determines the sign of `ext` by (repeated) squaring. More...

Sqrt_extension	abs () const
	returns the absolute value of `ext`. More...

CGAL::Comparison_result	compare (const Sqrt_extension &y, bool in_same_extension=!DifferentExtensionComparable::value) const
	Compares `ext` with y. More...

Sqrt_extension &	operator+= (const Sqrt_extension &a)

Sqrt_extension &	operator-= (const Sqrt_extension &a)

Sqrt_extension &	operator*= (const Sqrt_extension &a)

Sqrt_extension &	operator/= (const Sqrt_extension &a)