Fitting Algorithms

Available in MaCh3 fitting algorithms. More...

Classes
class	DelayedMR2T2
	Implementation of delayed rejection for MR2T2. More...
class	MinuitFit
	Implementation of Minuit fitting algorithm [18]. More...
class	MR2T2
	MCMC algorithm implementing the Metropolis–Rosenbluth–Rosenbluth–Teller–Teller (MR \(^2\)T \(^2\)) method. More...
class	PSO
	Class PSO, consist of a vector of object Class Particle and global best Takes in the size (number of particle) and number of iteration functions includes: finding global best, updating velocity, actual minimisation function. More...

Functions
std::unique_ptr< FitterBase >	MaCh3FitterFactory (Manager *FitManager)
	MaCh3 Factory initiates one of implemented fitting algorithms. More...

Detailed Description

Available in MaCh3 fitting algorithms.

Introduction

MaCh3 provides multiple fitting strategies that fall into two main categories: Markov Chain Monte Carlo samplers and likelihood minimisation algorithms.

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Markov Chain Monte Carlo (MCMC)

These algorithms explore parameter space by stochastic sampling of the posterior. They are primarily used for full Bayesian inference and high-dimensional problems.

Implemented methods:

• MR2T2 — Metropolis–Rosenbluth–Rosenbluth–Teller–Teller sampler.
• DelayedMR2T2 — Extension including delayed rejection to improve sampling efficiency and acceptance in difficult likelihood surfaces.

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Likelihood Minimizers

These algorithms deterministically minimise the negative log-likelihood to obtain a best-fit point. They are typically much faster than MCMC and are useful for diagnostics, validation, and systematic scans.

Implemented methods:

• MinuitFit — Gradient-based minimiser.
• PSO (Particle Swarm Optimisation) — Global optimisation using a swarm of walkers to locate the likelihood minimum.

Factory Method

A factory method is implemented to select the algorithm from the configuration file instead of hard-coding it.

Example configuration:

General:
  FittingAlgorithm: "MCMC"

or

General:
  FittingAlgorithm: "PSO"

This allows switching algorithms without recompilation.

Function Documentation

MaCh3FitterFactory()

std::unique_ptr<FitterBase> MaCh3FitterFactory

(

Manager *

FitManager

)

MaCh3 Factory initiates one of implemented fitting algorithms.

Parameters

FitManager

pointer to Manager class

Note

Example YAML configuration:

General:
  FittingAlgorithm: ["MCMC"]

Definition at line 5 of file MaCh3Factory.cpp.

                                                              {
// ********************************************
  std::unique_ptr<FitterBase> MaCh3Fitter = nullptr;
 
  auto Algorithm = GetFromManager<std::string>(fitMan->raw()["General"]["FittingAlgorithm"], "MCMC");
 
  if(Algorithm == "MCMC" || Algorithm == "MR2T2") 
  {
    MaCh3Fitter = std::make_unique<MR2T2>(fitMan);
  }
  else if (Algorithm == "DelayedMCMC"  || Algorithm == "DelayedMR2T2")
  {
    MaCh3Fitter = std::make_unique<DelayedMR2T2>(fitMan);
  }
  else if (Algorithm == "PSO")
  {
    MaCh3Fitter = std::make_unique<PSO>(fitMan);
  }
  else if (Algorithm == "Minuit2")
  {
    #ifdef MaCh3_MINUIT2
    MaCh3Fitter = std::make_unique<MinuitFit>(fitMan);
    #else
    MACH3LOG_ERROR("Trying to use Minuit2 however MaCh3 was compiled without Minuit2 support");
    throw MaCh3Exception(__FILE__ , __LINE__ );
    #endif
  }
  else
  {
    MACH3LOG_ERROR("You want to use algorithm {}, I don't recognize it, sry", Algorithm);
    throw MaCh3Exception(__FILE__ , __LINE__ );
  }
  return MaCh3Fitter;
}