MRBestFitPolynomial.h

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#pragma once
 
#include "MRMeshFwd.h"
#include <MRPch/MREigenCore.h>
 
#include <cstddef>
#include <vector>
#include <variant>
#include <optional>
 
 
namespace MR
{
 
 
constexpr bool canSolvePolynomial( auto degree )
{
    return 1 <= degree && degree <= 4;
}
 
constexpr bool canMinimizePolynomial( auto degree )
{
    return degree <= 5;
}
 
// Please note that these template classes are explicitly instantiated in the corresponding .cpp files.
// The following degrees are instantiated: [2; 6].
 
template <typename T, size_t degree>
struct Polynomial
{
    static constexpr size_t n = degree + 1;
    Eigen::Vector<T, n> a;
 
    template <typename NewT>
    Polynomial<NewT, degree> cast() const
    { return { a.template cast<NewT>() }; }
 
    MRMESH_API T operator() ( T x ) const;
 
    MRMESH_API std::vector<T> solve( T tol ) const
        requires ( canSolvePolynomial( degree ) );
 
    MRMESH_API Polynomial<T, degree == 0 ? 0 : degree - 1> deriv() const;
 
    MRMESH_API T intervalMin( T a, T b ) const
        requires ( canMinimizePolynomial( degree ) );
};
 
template <size_t degree>
using Polynomialf = Polynomial<float, degree>;
 
template <size_t degree>
using Polynomiald = Polynomial<double, degree>;
 
 
template <typename T>
using Polynomialx = std::variant
    < Polynomial<T, 0>
    , Polynomial<T, 1>
    , Polynomial<T, 2>
    , Polynomial<T, 3>
    , Polynomial<T, 4>
    , Polynomial<T, 5>
    , Polynomial<T, 6>
    >;
 
template <typename T>
struct PolynomialWrapper
{
    Polynomialx<T> poly;
 
    template <size_t degree>
    PolynomialWrapper( const Polynomial<T, degree>& p ):
        poly( p )
    {}
 
    MRMESH_API T operator() ( T x ) const;
 
    MRMESH_API PolynomialWrapper<T> deriv() const;
 
    MRMESH_API std::optional<T> intervalMin( T a, T b ) const;
};
 
using PolynomialWrapperf = PolynomialWrapper<float>;
using PolynomialWrapperd = PolynomialWrapper<double>;
 
 
template <typename T, size_t degree>
class BestFitPolynomial
{
public:
    MRMESH_API explicit BestFitPolynomial( T reg );
 
    MRMESH_API void addPoint( T x, T y );
 
    MRMESH_API void addPoint( T x, T y, T weight );
 
    MRMESH_API Polynomial<T, degree> getBestPolynomial() const;
 
private:
    static constexpr size_t n = degree + 1;
    T lambda_ {};
    Eigen::Matrix<T, n, n> XtX_;
    Eigen::Vector<T, n> XtY_;
    T sumWeight_ = 0;
};
 
template <size_t degree>
using BestFitPolynomialf = BestFitPolynomial<float, degree>;
 
template <size_t degree>
using BestFitPolynomiald = BestFitPolynomial<double, degree>;
 
 
 
}