ROOT   Reference Guide
ROOT::Minuit2::FCNBase Class Referenceabstract

Interface (abstract class) defining the function to be minimized, which has to be implemented by the user.

Definition at line 45 of file FCNBase.h.

## Public Member Functions

~FCNBase () override

virtual double ErrorDef () const
Error definition of the function. More...

double operator() (const std::vector< double > &v) const override=0
The meaning of the vector of parameters is of course defined by the user, who uses the values of those parameters to calculate their function Value. More...

virtual void SetErrorDef (double)
add interface to set dynamically a new error definition Re-implement this function if needed. More...

virtual double Up () const =0
Error definition of the function. More...

Public Member Functions inherited from ROOT::Minuit2::GenericFunction
virtual ~GenericFunction ()

virtual double operator() (const std::vector< double > &x) const =0
Evaluates the function using the vector containing the input values. More...

#include <Minuit2/FCNBase.h>

Inheritance diagram for ROOT::Minuit2::FCNBase:
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## ◆ ~FCNBase()

 ROOT::Minuit2::FCNBase::~FCNBase ( )
inlineoverride

Definition at line 48 of file FCNBase.h.

## ◆ ErrorDef()

 virtual double ROOT::Minuit2::FCNBase::ErrorDef ( ) const
inlinevirtual

Error definition of the function.

MINUIT defines Parameter errors as the change in Parameter Value required to change the function Value by up. Normally, for chisquared fits it is 1, and for negative log likelihood, its Value is 0.5. If the user wants instead the 2-sigma errors for chisquared fits, it becomes 4, as Chi2(x+n*sigma) = Chi2(x) + n*n.

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Definition at line 86 of file FCNBase.h.

## ◆ operator()()

 double ROOT::Minuit2::FCNBase::operator() ( const std::vector< double > & v ) const
overridepure virtual

The meaning of the vector of parameters is of course defined by the user, who uses the values of those parameters to calculate their function Value.

The order and the position of these parameters is strictly the one specified by the user when supplying the starting values for minimization. The starting values must be specified by the user, either via an std::vector<double> or the MnUserParameters supplied as input to the MINUIT minimizers such as VariableMetricMinimizer or MnMigrad. Later values are determined by MINUIT as it searches for the Minimum or performs whatever analysis is requested by the user.

Parameters
 v function parameters as defined by the user.
Returns
the Value of the function.
MnUserParameters
VariableMetricMinimizer

Implements ROOT::Minuit2::GenericFunction.

## ◆ SetErrorDef()

 virtual void ROOT::Minuit2::FCNBase::SetErrorDef ( double )
inlinevirtual

add interface to set dynamically a new error definition Re-implement this function if needed.

Definition at line 106 of file FCNBase.h.

## ◆ Up()

 virtual double ROOT::Minuit2::FCNBase::Up ( ) const
pure virtual

Error definition of the function.

MINUIT defines Parameter errors as the change in Parameter Value required to change the function Value by up. Normally, for chisquared fits it is 1, and for negative log likelihood, its Value is 0.5. If the user wants instead the 2-sigma errors for chisquared fits, it becomes 4, as Chi2(x+n*sigma) = Chi2(x) + n*n.

Libraries for ROOT::Minuit2::FCNBase:
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The documentation for this class was generated from the following file: