MVAPrototypeModule.cc

/**************************************************************************
 * basf2 (Belle II Analysis Software Framework)                           *
 * Author: The Belle II Collaboration                                     *
 *                                                                        *
 * See git log for contributors and copyright holders.                    *
 * This file is licensed under LGPL-3.0, see LICENSE.md.                  *
 **************************************************************************/
 
 
#include <mva/modules/MVAExpert/MVAPrototypeModule.h>
#include <mva/interface/Interface.h>
 
#include <memory>
 
using namespace Belle2;
 
REG_MODULE(MVAPrototype);
 
MVAPrototypeModule::MVAPrototypeModule() : Module()
{
  setDescription("Prototype of a module which uses the MVA package");
 
  // Usually it is save to execute the MVA expert in Parallel mode,
  // but ultimately this depends on the backend you use.
  // The default method FastBDT has no problem with parallel execution.
  setPropertyFlags(c_ParallelProcessingCertified);
 
  // Your module probably has a parameter which defines the database identifier or filename of the mva weightfile.
  // Of course you could also hard-code it in the source code if this is not configurable
  addParam("identifier", m_identifier, "The database identifier or filename which is used to load the weights during the training.");
 
  // For classification it is often useful to be able to change the signalFraction.
  // If the signal fraction in the training is different from the dataset you want to apply it to,
  // you have to pass the correct signalFraction otherwise you cannot interpret the output of the classifier as a probability.
  // On the other hand, if you don't require the output to be a probability you don't have to care about this.
  addParam("signalFraction", m_signal_fraction_override,
           "signalFraction to calculate probability (if -1 the signalFraction of the training data is used)", -1.0);
}
 
void MVAPrototypeModule::initialize()
{
  // If the identifier does not end on .root or .xml, we are dealing with a database identifier
  // so we need to create a DBObjPtr, which will fetch the weightfile from the database
  if (not(m_identifier.ends_with(".root") or m_identifier.ends_with(".xml"))) {
    m_weightfile_representation = std::make_unique<DBObjPtr<DatabaseRepresentationOfWeightfile>>(m_identifier);
  }
 
  // The supported methods have to be initialized once (calling it more than once is save)
  MVA::AbstractInterface::initSupportedInterfaces();
 
}
 
void MVAPrototypeModule::beginRun()
{
 
  // If the DBObjPtr is valid we are dealing with a weightfile from the database
  if (m_weightfile_representation) {
    // We check if the weightfile changed and we have to update the expert
    if (m_weightfile_representation->hasChanged()) {
      // The actual weightfile is stored in the m_data field of the m_weightfile_representation
      std::stringstream ss((*m_weightfile_representation)->m_data);
      auto weightfile = MVA::Weightfile::loadFromStream(ss);
      init_mva(weightfile);
    }
    // In case of a file-based weightfile we load it here
    // in principal this could be done in initialize as well
  } else {
    auto weightfile = MVA::Weightfile::loadFromFile(m_identifier);
    init_mva(weightfile);
  }
 
}
 
void MVAPrototypeModule::init_mva(MVA::Weightfile& weightfile)
{
  // This function initializes the MVA::Expert using the provided weightfile
 
  // First we get the GeneralOptions from the weightfile
  // and update the signal_fraction if required
  MVA::GeneralOptions general_options;
  weightfile.getOptions(general_options);
  if (m_signal_fraction_override > 0)
    weightfile.addSignalFraction(m_signal_fraction_override);
 
  // Secondly we load all supported interfaces, and fetch the correct MVA::Expert
  // and load the weightfile into this expert
  auto supported_interfaces = MVA::AbstractInterface::getSupportedInterfaces();
  m_expert = supported_interfaces[general_options.m_method]->getExpert();
  m_expert->load(weightfile);
 
  // Finally, we create an MVA::SingleDataset, in which we will save our features later
  // to pass them to the expert.
  // If you want to apply the expert to more than one sample, you can also use
  // MVA::MultiDataset or any other Dataset defined by the mva package interface.
  std::vector<float> dummy(general_options.m_variables.size(), 0);
  m_dataset = std::make_unique<MVA::SingleDataset>(general_options, dummy, 0);
 
}
 
void MVAPrototypeModule::event()
{
  // Just to be save we check again if the MVA::Expert is loaded
  // It can happen that for example the database doesn't find the payload
  // and the expert ends up uninitialized.
  if (not m_expert) {
    B2ERROR("MVA Expert is not loaded! I will return 0");
    return;
  }
 
  // You have to fill the dataset with your data.
  // The order must be the same as the order of the variables in general_options.m_variables
  for (unsigned int i = 0; i < m_dataset->getNumberOfFeatures(); ++i) {
    m_dataset->m_input[i] = 1.0;
  }
 
  // All what is left to do is applying the expert to the dataset
  // it will return an std::vector with the results, with one entry per sample.
  // The MVA::SingleDataset only contains one entry, so we are interested only in the first entry here.
  // The MVA::MultiDataset on the other hand would have more than one entry in the returned vector of apply.
  float probability = m_expert->apply(*m_dataset)[0];
  B2INFO("The probability is " << probability);
}