Interpolation.hpp

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#pragma once
 
#include <polyfem/Common.hpp>
 
#include <memory>
#include <vector>
 
namespace polyfem::utils
{
    class Interpolation
    {
    public:
        virtual ~Interpolation() {}
        virtual double eval(const double t) const = 0;
        virtual void init(const json &params) {}
 
        static std::shared_ptr<Interpolation> build(const json &params);
    };
 
    class NoInterpolation : public Interpolation
    {
    public:
        double eval(const double t) const override { return 1; };
    };
 
    class LinearInterpolation : public Interpolation
    {
    public:
        double eval(const double t) const override { return t; }
    };
 
    class LinearRamp : public Interpolation
    {
    public:
        double eval(const double t) const override;
        void init(const json &params) override;
 
    private:
        double to_;
        double from_;
    };
 
    class PiecewiseInterpolation : public Interpolation
    {
    public:
        virtual void init(const json &params) override;
        double eval(const double t) const override;
        double extend(const double t) const;
 
    public:
        std::vector<double> points_;
        std::vector<double> values_;
 
        enum class Extend
        {
            CONSTANT,
            EXTRAPOLATE,
            REPEAT,
            REPEAT_OFFSET
        };
        Extend extend_;
 
    protected:
        virtual double eval_piece(const double t, const int i) const = 0;
 
        double dy_dt(const double t) const;
        virtual double dy_dt_piece(const double t, const int i) const = 0;
    };
 
    class PiecewiseConstantInterpolation : public PiecewiseInterpolation
    {
    protected:
        double eval_piece(const double t, const int i) const override { return values_[i]; }
        double dy_dt_piece(const double t, const int i) const override { return 0; }
    };
 
    class PiecewiseLinearInterpolation : public PiecewiseInterpolation
    {
    protected:
        double eval_piece(const double t, const int i) const override;
        double dy_dt_piece(const double t, const int i) const override;
    };
 
    class PiecewiseCubicInterpolation : public PiecewiseInterpolation
    {
    public:
        void init(const json &params) override;
 
        const Eigen::MatrixXd &coeffs() const { return coeffs_; }
 
    protected:
        double eval_piece(const double t, const int i) const override;
        double dy_dt_piece(const double t, const int i) const override;
 
        Eigen::MatrixXd coeffs_;
    };
 
} // namespace polyfem::utils