CGAL::Arr_rational_function_traits_2< AlgebraicKernel_d_1 > Class Template Reference

#include <CGAL/Arr_rational_function_traits_2.h>

Definition

The traits class Arr_rational_function_traits_2 is a model of the ArrangementTraits_2 concept.

It handles bounded and unbounded arcs of rational functions, referred to as rational arcs (in particular, such an arc may correspond to the entire graph of a rational function). It supports bounded and unbounded arcs. Thus, it is also a model of the concept ArrangementOpenBoundaryTraits_2. The traits class enables the construction and maintenance of arrangements of such arcs.

A rational function \( y = \frac{P(x)}{Q(x)}\) is defined by two polynomials \( P\) and \( Q\) of arbitrary degrees. If \( Q(x) = 1\) then the function is a simple polynomial function. Usually the domain is \( \mathbb{R}\) but the function may also be restricted to a bounded interval \( [x_{\rm min}, x_{\rm max}]\) or defined over a ray \( (-\infty, x_{\rm max}]\) or over \( [x_{\rm min}, \infty)\). Rational functions are represented by the nested type Curve_2. Note that a rational function may be not continuous since roots of \( Q\) induce vertical asymptotes, which would contradict the notion of an \( x\)-monotone curve as it is introduced by the ArrangementTraits_2 concept. Thus, continuous portions of rational functions are represented by the nested type X_monotone_curve_2, which is different from Curve_2. Constructors for both classes are provided by the traits. A Curve_2 may be split up into several X_monotone_curve_2 using Make_x_monotone_2.

The template parameter of the traits must be a model of the concept AlgebraicKernel_d_1. A rational function is then represented by two polynomials \( P\) and \( Q\) of type AlgebraicKernel_d_1::Polynomial_1. A point is represented by a rational function and its \( x\)-coordinate, which is of type AlgebraicKernel_d_1::Algebraic_real_1. Note that an explicit representation of the \( y\)-coordinate is only computed upon request, which can be a rather costly operation.

The constructed rational functions are cached by the traits class. The cache is local to each traits class object. It is therefore necessary to construct the curves using the constructor objects provided by member functions of the traits class. Moreover, a curve must only be used with its own traits. The cache is automatically cleaned up from time to time. The amortized clean up costs are constant. However, there is also a separate member function that cleans up the cache on demand.

While Arr_rational_function_traits_2 models the concept ArrangementDirectionalXMonotoneTraits_2, the implementation of the Are_mergeable_2 operation does not enforce the input curves to have the same direction as a precondition. Moreover, Arr_rational_function_traits_2 supports the merging of curves of opposite directions.

Is Model Of:

ArrangementTraits_2

ArrangementDirectionalXMonotoneTraits_2

ArrangementOpenBoundaryTraits_2

Examples:

Arrangement_on_surface_2/rational_functions.cpp, and Arrangement_on_surface_2/unbounded_rational_functions.cpp.

Classes
class	Construct_curve_2
	Functor to construct a Curve_2. More...
class	Construct_x_monotone_curve_2
	Functor to construct a X_monotone_curve_2. More...
class	Curve_2
	The Curve_2 class nested within the traits is used to represent rational functions which may be restricted to a certain x-range. More...
class	Point_2
class	X_monotone_curve_2
	The X_monotone_curve_2 class nested within the traits is used to represent \( x\)-monotone parts of rational functions. More...

Types
typedef AlgebraicKernel_d_1	Algebraic_kernel_d_1
typedef AlgebraicKernel_d_1::Coefficient	Coefficient
typedef AlgebraicKernel_d_1::Polynomial_1	Polynomial_1
typedef AlgebraicKernel_d_1::Algebraic_real_1	Algebraic_real_1
typedef AlgebraicKernel_d_1::Bound	Bound

Creation
	Arr_rational_function_traits_2 (const Algebraic_kernel_d_1 *kernel)
	constructs an empty traits that uses the kernel pointed by kernel for performing algebraic operations.

Operations
Construct_curve_2	construct_curve_2_object () const
	Returns an instance of Construct_curve_2.
Construct_x_monotone_curve_2	construct_x_monotone_curve_2_object () const
	Returns an instance of Construct_x_monotone_curve_2.
void	cleanup_cache () const
	Deletes all curves from the cache that exist only there.
const Algebraic_kernel_d_1 *	algebraic_kernel_d_1 () const
	Returns a pointer to the used algerbaic kernel object.