InverseFunction.h

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#ifndef __INVERSE_FUNCTION_H
#define __INVERSE_FUNCTION_H

#include "../../Core/Functions.h"
#include "../../Core/InterpSolutionIterator.h"
#include <gsl/gsl_roots.h>

class InverseFunction : public Core::OneArgumentDiffFunction {
private:
    const Core::OneArgumentDiffFunction &__to_invert;

    double __tolerance;

    gsl_root_fsolver *__solver;

    gsl_function_fdf __solver_fdf;

    gsl_function __solver_f;

    mutable double __target;

    double __search_min, __search_max;

    friend double gsl_f(double x, void *params);

    friend double gsl_df(double x, void *params);

    friend void gsl_fdf(double x, void *params, double *f, double *df);

public:
    InverseFunction(const OneArgumentDiffFunction &to_invert,
                    double search_min,
                    double search_max,
                    double tolerance = 1e-10);

    double operator()(double x) const;

    double range_high() const
    {
        throw Core::Error::Runtime(
            "Upper end of inverse function range is unknown."
        );
    }

    double range_low() const
    {
        throw Core::Error::Runtime(
            "Lower end of inverse function range is unknown."
        );
    }

    Core::InterpSolutionIterator crossings(double = 0) const
    {
        throw Core::Error::Runtime(
            "Finding all solutinos of an inverse function not implemented."
        );
    };

    const Core::FunctionDerivatives *deriv(double x) const;

    ~InverseFunction();
};

#endif