SuaveIntegrator.cpp

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/*
 *  CepGen: a central exclusive processes event generator
 *  Copyright (C) 2021-2024  Laurent Forthomme
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#include "CepGen/Core/Exception.h"
#include "CepGen/Integration/Integrand.h"
#include "CepGen/Modules/IntegratorFactory.h"
#include "CepGenAddOns/CubaWrapper/Integrator.h"
#include "cuba.h"
 
namespace cepgen {
  namespace cuba {
    class SuaveIntegrator : public Integrator {
    public:
      explicit SuaveIntegrator(const ParametersList& params)
          : Integrator(params),
            nnew_(steer<int>("NNew")),
            nmin_(steer<int>("NMin")),
            flatness_(steer<double>("Flatness")) {
        CG_DEBUG("Integrator:build") << "Cuba-Suave integrator built.";
      }
 
      static ParametersDescription description() {
        auto desc = Integrator::description();
        desc.setDescription("Cuba implementation of the Suave algorithm");
        desc.add<int>("NNew", 1000).setDescription("number of new integrand evaluations in each subdivision");
        desc.add<int>("NMin", 2).setDescription(
            "minimum number of samples a former pass must contribute to a subregion to be considered in that region’s "
            "compound integral value");
        desc.add<double>("Flatness", 50.).setDescription("type of norm used to compute the fluctuation of a sample");
        return desc;
      }
 
      Value integrate() override {
        int neval, fail, nregions;
        double integral, error, prob;
 
        Suave(gIntegrand->size(),
              ncomp_,
              cuba_integrand,
              nullptr,
              nvec_,
              epsrel_,
              epsabs_,
              verbose_,
              rnd_gen_->parameters().get<unsigned long long>("seed"),
              mineval_,
              maxeval_,
              nnew_,
              nmin_,
              flatness_,
              nullptr,  // const char* statefile
              nullptr,  // void* spin
              &nregions,
              &neval,
              &fail,
              &integral,
              &error,
              &prob);
        return Value{integral, error};
      }
 
    private:
      const int nnew_, nmin_;
      const double flatness_;
    };
  }  // namespace cuba
}  // namespace cepgen
using SuaveIntegratorCuba = cepgen::cuba::SuaveIntegrator;
REGISTER_INTEGRATOR("cuba_suave", SuaveIntegratorCuba);