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 // This file is part of the Acts project.
 //
 // Copyright (C) 2018 CERN for the benefit of the Acts project
 //
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 #include "Acts/Definitions/TrackParametrization.hpp"
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/MagneticField/BFieldMapUtils.hpp"
 #include "Acts/MagneticField/InterpolatedBFieldMap.hpp"
 #include "Acts/MagneticField/SolenoidBField.hpp"
 #include "Acts/Tests/CommonHelpers/BenchmarkTools.hpp"
 #include "Acts/Utilities/VectorHelpers.hpp"
 
 #include <chrono>
 #include <fstream>
 #include <iostream>
 #include <random>
 #include <string>
 
 using namespace Acts::UnitLiterals;
 
 int main(int argc, char* argv[]) {
   std::size_t iters_map = 5e2;
   std::size_t iters_solenoid = 3;
   std::size_t runs_solenoid = 1000;
   if (argc >= 2) {
     iters_map = std::stoi(argv[1]);
   }
   if (argc >= 3) {
     iters_solenoid = std::stoi(argv[2]);
   }
   if (argc >= 4) {
     runs_solenoid = std::stoi(argv[3]);
   }
 
   const double L = 5.8_m;
   const double R = (2.56 + 2.46) * 0.5 * 0.5_m;
   const std::size_t nCoils = 1154;
   const double bMagCenter = 2_T;
   const std::size_t nBinsR = 150;
   const std::size_t nBinsZ = 200;
 
   double rMin = -0.1;
   double rMax = R * 2.;
   double zMin = 2 * (-L / 2.);
   double zMax = 2 * (L / 2.);
 
   Acts::SolenoidBField bSolenoidField({R, L, nCoils, bMagCenter});
   std::cout << "Building interpolated field map" << std::endl;
   auto bFieldMap = Acts::solenoidFieldMap({rMin, rMax}, {zMin, zMax},
                                           {nBinsR, nBinsZ}, bSolenoidField);
   Acts::MagneticFieldContext mctx{};
 
   std::minstd_rand rng;
   std::uniform_real_distribution<double> zDist(1.5 * (-L / 2.), 1.5 * L / 2.);
   std::uniform_real_distribution<double> rDist(0, R * 1.5);
   std::uniform_real_distribution<double> phiDist(-M_PI, M_PI);
   auto genPos = [&]() -> Acts::Vector3 {
     const double z = zDist(rng), r = rDist(rng), phi = phiDist(rng);
     return {r * std::cos(phi), r * std::sin(phi), z};
   };
 
   std::ofstream os{"bfield_bench.csv"};
 
   auto csv = [&](const std::string& name, auto res) {
     os << name << "," << res.run_timings.size() << "," << res.iters_per_run
        << "," << res.totalTime().count() << "," << res.runTimeMedian().count()
        << "," << 1.96 * res.runTimeError().count() << ","
        << res.iterTimeAverage().count() << ","
        << 1.96 * res.iterTimeError().count();
 
     os << std::endl;
   };
 
   os << "name,runs,iters,total_time,run_time_median,run_time_error,iter_"
         "time_average,iter_time_error"
      << std::endl;
 
   // SolenoidBField lookup is so slow that the cost of generating a random field
   // lookup position is negligible in comparison...
   std::cout << "Benchmarking random SolenoidBField lookup: " << std::flush;
   const auto solenoid_result = Acts::Test::microBenchmark(
       [&] { return bSolenoidField.getField(genPos()); }, iters_solenoid,
       runs_solenoid);
   std::cout << solenoid_result << std::endl;
   csv("solenoid", solenoid_result);
 
   // ...but for interpolated B-field map, the overhead of a field lookup is
   // comparable to that of generating a random position, so we must be more
   // careful. Hence we do two microbenchmarks which represent a kind of
   // lower and upper bound on field lookup performance.
   //
   // - The first benchmark operates at constant position, so it measures only
   //   field lookup overhead but has unrealistically good cache locality. In
   //   that sense, it provides a lower bound of field lookup performance.
   std::cout << "Benchmarking interpolated field lookup: " << std::flush;
   const auto fixedPos = genPos();
   const auto map_fixed_nocache_result = Acts::Test::microBenchmark(
       [&] { return bFieldMap.getField(fixedPos); }, iters_map);
   std::cout << map_fixed_nocache_result << std::endl;
   csv("interp_nocache_fixed", map_fixed_nocache_result);
 
   std::cout << "Benchmarking random interpolated field lookup: " << std::flush;
 
   // - The second benchmark generates random positions, so it is biased by the
   //   cost of random position generation and has unrealistically bad cache
   //   locality, but provides an upper bound of field lookup performance.
   const auto map_rand_result = Acts::Test::microBenchmark(
       [&] { return bFieldMap.getField(genPos()); }, iters_map);
   std::cout << map_rand_result << std::endl;
   csv("interp_nocache_random", map_rand_result);
 
   // - This variation of the first benchmark uses a fixed position again, but
   //   uses the cache infrastructure to evaluate how much of an impact it has on
   //   performance in this scenario. We expect this to improve performance as
   //   the cache will always be valid for the fixed point.
   {
     std::cout << "Benchmarking cached interpolated field lookup: "
               << std::flush;
     auto cache = bFieldMap.makeCache(mctx);
     const auto map_cached_result_cache = Acts::Test::microBenchmark(
         [&] { return bFieldMap.getField(fixedPos, cache).value(); }, iters_map);
     std::cout << map_cached_result_cache << std::endl;
     csv("interp_cache_fixed", map_cached_result_cache);
   }
 
   // - This variation of the second benchmark again generates random positions
   //   and uses the cache infrastructure to evaluate the impact on performance.
   //   We expect this to deteriorate performance, as the cache will most likely
   //   be invalid and need to be recreated, on top of the underlying lookup.
   {
     std::cout << "Benchmarking cached random interpolated field lookup: "
               << std::flush;
     auto cache2 = bFieldMap.makeCache(mctx);
     const auto map_rand_result_cache = Acts::Test::microBenchmark(
         [&] { return bFieldMap.getField(genPos(), cache2).value(); },
         iters_map);
     std::cout << map_rand_result_cache << std::endl;
     csv("interp_cache_random", map_rand_result_cache);
   }
 
   // - The fourth benchmark tests a more 'realistic' access pattern than fixed
   //   or random positions: it advances along a straight line (which is close to
   //   a slightly curved line which happens in particle propagation). This
   //   instance does not use the cache infrastructure, so is effectively close
   //   to the random points benchmark, although positions are not really random.
   {
     std::cout << "Benchmarking advancing interpolated field lookup: "
               << std::flush;
     Acts::Vector3 pos{0, 0, 0};
     Acts::Vector3 dir{};
     dir.setRandom();
     double h = 1e-3;
     std::vector<Acts::Vector3> steps;
     steps.reserve(iters_map);
     for (std::size_t i = 0; i < iters_map; i++) {
       pos += dir * h;
       double z = pos[Acts::eFreePos2];
       if (Acts::VectorHelpers::perp(pos) > rMax || z >= zMax || z < zMin) {
         break;
       }
       steps.push_back(pos);
     }
     const auto map_adv_result = Acts::Test::microBenchmark(
         [&](const auto& s) { return bFieldMap.getField(s); }, steps);
     std::cout << map_adv_result << std::endl;
     csv("interp_nocache_adv", map_adv_result);
 
     // - This variation of the fourth benchmark advances in a straight line, but
     //   also uses the cache infrastructure. As subsequent positions are close
     //   to one another, the cache will be valid for a certain number of points,
     //   before becoming invalid. This means we expect performance to improve
     //   over the uncached straight line advance.
 
     std::cout << "Benchmarking cached advancing interpolated field lookup: "
               << std::flush;
     auto cache = bFieldMap.makeCache(mctx);
     const auto map_adv_result_cache = Acts::Test::microBenchmark(
         [&](const auto& s) { return bFieldMap.getField(s, cache).value(); },
         steps);
     std::cout << map_adv_result_cache << std::endl;
     csv("interp_cache_adv", map_adv_result_cache);
   }
 }

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