CGAL 4.14 - 2D Arrangements
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_1algebraic_kernel_d_1 () const
Returns a pointer to the used algerbaic kernel object.