CGAL 6.1.2 - 2D Arrangements: CGAL::Arr_rational_function_traits_2< AlgebraicKernel_d_1 > Class Template Reference

CGAL 6.1.2 - 2D Arrangements

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CGAL::Arr_rational_function_traits_2< AlgebraicKernel_d_1 > Class Template Reference
Reference Manual » Geometry Traits Classes

`#include <CGAL/Arr_rational_function_traits_2.h>`

## Definition

template<typename AlgebraicKernel_d_1>
class CGAL::Arr_rational_function_traits_2< AlgebraicKernel_d_1 >

The traits class `Arr_rational_function_traits_2` is a model of the `AosTraits_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 `AosOpenBoundaryTraits_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 `AosTraits_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 `AosDirectionalXMonotoneTraits_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
  `AosTraits_2`
  `AosDirectionalXMonotoneTraits_2`
  `AosOpenBoundaryTraits_2`

## 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 algebraic kernel object.