Integrator.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 "CepGenAddOns/CubaWrapper/Integrator.h"
 
namespace cepgen {
  namespace cuba {
    Integrand* Integrator::gIntegrand = nullptr;
 
    Integrator::Integrator(const ParametersList& params)
        : cepgen::Integrator(params),
          ncomp_(steer<int>("ncomp")),
          nvec_(steer<int>("nvec")),
          epsrel_(steer<double>("epsrel")),
          epsabs_(steer<double>("epsabs")),
          mineval_(steer<int>("mineval")),
          maxeval_(steer<int>("maxeval")),
          verbose_(steer<int>("verbose")) {}
 
    Value Integrator::integrate(Integrand& integr) {
      gIntegrand = &integr;
      return integrate();
    }
 
    ParametersDescription Integrator::description() {
      auto desc = cepgen::Integrator::description();
      desc.setDescription("Cuba generic integration algorithm");
      desc.add<int>("ncomp", 1).setDescription("number of components of the integrand");
      desc.add<int>("nvec", 1).setDescription("number of samples received by the integrand");
      desc.add<double>("epsrel", 1.e-3).setDescription("requested relative accuracy");
      desc.add<double>("epsabs", 1.e-12).setDescription("requested absolute accuracy");
      desc.add<int>("mineval", 0).setDescription("minimum number of integrand evaluations required");
      desc.add<int>("maxeval", 50'000).setDescription("(approximate) maximum number of integrand evaluations allowed");
      desc.add<int>("verbose", 0);
      return desc;
    }
 
    int cuba_integrand(const int* ndim, const double xx[], const int* /*ncomp*/, double ff[], void* /*userdata*/) {
      if (!Integrator::gIntegrand)
        throw CG_FATAL("cuba_integrand") << "Integrand not set for the Cuba algorithm!";
      //TODO: handle the non-[0,1] ranges
      ff[0] = Integrator::gIntegrand->eval(std::vector<double>(xx, xx + *ndim));
      return 0;
    }
  }  // namespace cuba
}  // namespace cepgen