# It seems like a easy problem with the code(C++ROOT) from chatgpt

ROOT Version: 6.24/06

code:
#include
#include “TF1.h”
#include “TCanvas.h”
#include “Math/Minimizer.h”
#include “Math/Factory.h”
#include “Math/Functor.h”
#include

// 定义方程N(x)
double N(double x, const double* params) {
double A = params[0];
double B = params[1];
return A * std::exp(B * x);
}

// 定义方程Y(x)
double Y(double x, const double* params) {
double C = params[2];
double D = params[3];
double E = params[4];
double F = params[5];
return C * (1 - std::exp(D + x)) + E * (1 - std::exp(F - x));
}

// 定义目标函数，用于寻找N(Y)的关系
double TargetFunction(const double* x, const double* params) {
return N(Y(x[0], params), params) - x[1];
}

int ss() {
// 创建TF1对象
TF1 *nFunc = new TF1(“nFunc”, N, 0, 10, 2);
TF1 *yFunc = new TF1(“yFunc”, Y, 0, 10, 6);

``````// 设置参数初始值
double params[6] = {2.0, 0.5, 1.0, 0.1, 0.8, 0.2}; // 这里使用示例参数

// 使用ROOT的数值优化器查找N(Y)的关系
ROOT::Math::Functor fcn(&TargetFunction, 2);
minimizer->SetFunction(fcn);
minimizer->SetLimitedVariable(0, "x", 0.0, 0.01, 0.0, 10.0);

minimizer->Minimize();

// 获取最优参数
const double* bestFitParams = minimizer->X();
double newY = N(Y(bestFitParams[0], params), params);

std::cout << "Best-fit parameter for x: " << bestFitParams[0] << std::endl;
std::cout << "N(Y) value: " << newY << std::endl;

delete nFunc;
delete yFunc;
delete minimizer;

return 0;
``````

}

error:

root [0]
Processing ss.C…
In module ‘Hist’:
/opt/root/include/TF1.h:732:104: error: type ‘double (double, const double )’ cannot be used prior to ‘::’ because it has no members
using Fnc_t = typename ROOT::Internal::GetFunctorType<decltype(ROOT::Internal::GetTheRightOp(&Func::operator()))>::type;
^
/opt/root/include/TF1.h:376:41: note: in instantiation of member function 'ROOT::Internal::TF1Builder<double (
)(double, const double )>::Build’ requested here
ROOT::Internal::TF1Builder::Build(this, f);
^
/home/geant4/root/SPEC/ss.C:32:22: note: in instantiation of function template specialization 'TF1::TF1<double (
)(double, const double *)>’ requested here
TF1 nFunc = new TF1(“nFunc”, N, 0, 10, 2);
^
In module ‘MathCore’:
/opt/root/include/Math/ParamFunctor.h:124:22: error: cannot initialize a parameter of type ‘double’ with an rvalue of type 'int
return (f)((T)x, (double
)p);
^~~~~
/opt/root/include/Math/ParamFunctor.h:94:45: note: in instantiation of member function 'ROOT::Math::ParamFunctorHandler<ROOT::Math::ParamFunctorTempl, double (
)(double, const double )>::FuncEvaluator<double ()(double, const double ), int>::EvalConst’ requested here
return FuncEvaluator<Func, EvalType>::EvalConst(fFunc,x,p);
^
/opt/root/include/Math/ParamFunctor.h:72:4: note: in instantiation of member function 'ROOT::Math::ParamFunctorHandler<ROOT::Math::ParamFunctorTempl, double (
)(double, const double )>::operator()’ requested here
ParamFunctorHandler(const Func & fun) : fFunc(fun) {}
^
/opt/root/include/Math/ParamFunctor.h:303:17: note: in instantiation of member function 'ROOT::Math::ParamFunctorHandler<ROOT::Math::ParamFunctorTempl, double (
)(double, const double )>::ParamFunctorHandler’ requested here
fImpl(new ParamFunctorHandler<ParamFunctorTempl,Func>(f) )
^
/opt/root/include/TF1.h:734:66: note: in instantiation of function template specialization 'ROOT::Math::ParamFunctorTempl::ParamFunctorTempl<double (
)(double, const double )>’ requested here
f->fFunctor.reset(new TF1::TF1FunctorPointerImpl<Fnc_t>(ROOT::Math::ParamFunctorTempl<Fnc_t>(func)));
^
/opt/root/include/TF1.h:376:41: note: in instantiation of member function 'ROOT::Internal::TF1Builder<double (
)(double, const double )>::Build’ requested here
ROOT::Internal::TF1Builder::Build(this, f);
^
/home/geant4/root/SPEC/ss.C:32:22: note: in instantiation of function template specialization 'TF1::TF1<double (
)(double, const double *)>’ requested here
TF1 *nFunc = new TF1(“nFunc”, N, 0, 10, 2);
^
In module ‘MathCore’:
/opt/root/include/Math/ParamFunctor.h:120:22: error: cannot initialize a parameter of type ‘double’ with an lvalue of type ‘int *’
return (f)(x, p);
^
/opt/root/include/Math/ParamFunctor.h:90:45: note: in instantiation of member function 'ROOT::Math::ParamFunctorHandler<ROOT::Math::ParamFunctorTempl, double (
)(double, const double )>::FuncEvaluator<double ()(double, const double ), int>::Eval’ requested here
return FuncEvaluator<Func, EvalType>::Eval(fFunc,x,p);
^
/opt/root/include/Math/ParamFunctor.h:72:4: note: in instantiation of member function 'ROOT::Math::ParamFunctorHandler<ROOT::Math::ParamFunctorTempl, double (
)(double, const double )>::operator()’ requested here
ParamFunctorHandler(const Func & fun) : fFunc(fun) {}
^
/opt/root/include/Math/ParamFunctor.h:303:17: note: in instantiation of member function 'ROOT::Math::ParamFunctorHandler<ROOT::Math::ParamFunctorTempl, double (
)(double, const double )>::ParamFunctorHandler’ requested here
fImpl(new ParamFunctorHandler<ParamFunctorTempl,Func>(f) )
^
/opt/root/include/TF1.h:734:66: note: in instantiation of function template specialization 'ROOT::Math::ParamFunctorTempl::ParamFunctorTempl<double (
)(double, const double )>’ requested here
f->fFunctor.reset(new TF1::TF1FunctorPointerImpl<Fnc_t>(ROOT::Math::ParamFunctorTempl<Fnc_t>(func)));
^
/opt/root/include/TF1.h:376:41: note: in instantiation of member function 'ROOT::Internal::TF1Builder<double (
)(double, const double )>::Build’ requested here
ROOT::Internal::TF1Builder::Build(this, f);
^
/home/geant4/root/SPEC/ss.C:32:22: note: in instantiation of function template specialization 'TF1::TF1<double (
)(double, const double *)>’ requested here
TF1 nFunc = new TF1(“nFunc”, N, 0, 10, 2);
^
In module ‘MathCore’:
/opt/root/include/Math/Functor.h:120:21: error: too few arguments to function call, expected 2, have 1
return fFunc(x);
~~~~~ ^
/opt/root/include/Math/Functor.h:90:4: note: in instantiation of member function 'ROOT::Math::FunctorHandler<ROOT::Math::Functor, double (
)(const double *, const double )>::DoEval’ requested here
FunctorHandler(unsigned int dim, const Func & fun ) :
^
/opt/root/include/Math/Functor.h:428:17: note: in instantiation of member function 'ROOT::Math::FunctorHandler<ROOT::Math::Functor, double (
)(const double *, const double )>::FunctorHandler’ requested here
fImpl(new FunctorHandler<Functor,Func>(dim,f) )
^
/home/geant4/root/SPEC/ss.C:39:25: note: in instantiation of function template specialization 'ROOT::Math::Functor::Functor<double (
)(const double *, const double *)>’ requested here
ROOT::Math::Functor fcn(&TargetFunction, 2);

Welcome to the ROOT forum

The code you posted doesn’t seem to match the error messages you get. It seems you are executing the macro `ss.C` but your code doesn’t have any `ss` function. Plus, your code has a `main` function which is not recommended in a ROOT script.

This is my first time using this feature so there were some problems and I have re-edited it

I cleaned up a bit:

``````#include "TF1.h"
#include "TCanvas.h"
#include "Math/Minimizer.h"
#include "Math/Factory.h"
#include "Math/Functor.h"

// 定义方程N(x)
double N(double x, const double* params) {
double A = params[0];
double B = params[1];
return A * std::exp(B * x);
}

// 定义方程Y(x)
double Y(double x, const double* params) {
double C = params[2];
double D = params[3];
double E = params[4];
double F = params[5];
return C * (1 - std::exp(D + x)) + E * (1 - std::exp(F - x));
}

// 定义目标函数，用于寻找N(Y)的关系
double TargetFunction(const double* x, const double* params) {
return N(Y(x[0], params), params) - x[1];
}

void ss() {
// 创建TF1对象
TF1 *nFunc = new TF1("nFunc", N, 0, 10, 2);
TF1 *yFunc = new TF1("yFunc", Y, 0, 10, 6);

// 设置参数初始值
double params[6] = {2.0, 0.5, 1.0, 0.1, 0.8, 0.2}; // 这里使用示例参数

// 使用ROOT的数值优化器查找N(Y)的关系
ROOT::Math::Functor fcn(&TargetFunction, 2);
minimizer->SetFunction(fcn);
minimizer->SetLimitedVariable(0, "x", 0.0, 0.01, 0.0, 10.0);

minimizer->Minimize();

// 获取最优参数
const double* bestFitParams = minimizer->X();
double newY = N(Y(bestFitParams[0], params), params);

std::cout << "Best-fit parameter for x: " << bestFitParams[0] << std::endl;
std::cout << "N(Y) value: " << newY << std::endl;

delete nFunc;
delete yFunc;
delete minimizer;
}
``````

Now I get:

``````root [0]
Processing ss.C...
In file included from input_line_9:1:
ROOT::Math::Functor fcn(&TargetFunction, 2);
^   ~~~~~~~~~~~~~~~~~~

``````

You should go back to the doc and find out the valid constructors.

I copied your code and reported the same error after running it (the same error as mine before but not the same error as yours), is there something wrong with my database?

Anyway, thank you for your reply, I will try another way to solve the problem, thank you for your help for me as a novice! Have a good day!

Ok, anyway you have the wrong ctor according to the macro I ran.

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