schelling_segregation.cc

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
*/
 
#include <cstddef>
#include <cstdint>
#include <filesystem>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <random>
 
#include <reproductions/ca_reproduction_support.H>
#include <tpl_ca_stochastic_rules.H>
 
using namespace Aleph::CA;
using namespace Aleph::CA::Reproductions;
 
#ifndef ALEPH_REPRODUCTIONS_SOURCE_DIR
# define ALEPH_REPRODUCTIONS_SOURCE_DIR "reproductions"
#endif
 
namespace
{
 
using Grid = Lattice<Dense_Cell_Storage<int, 2>, ToroidalBoundary>;
 
void seed_population(Grid &grid, const std::uint32_t seed)
{
  std::mt19937 rng(seed);
  std::discrete_distribution<int> pick({0.10, 0.45, 0.45});
  for (ca_size_t r = 0; r < grid.size(0); ++r)
    for (ca_size_t c = 0; c < grid.size(1); ++c)
      grid.set({static_cast<ca_index_t>(r), static_cast<ca_index_t>(c)}, pick(rng));
}
 
}  // namespace
 
int main()
{
  constexpr ca_size_t side = 100;
  constexpr std::size_t steps = 200;
  constexpr double threshold = 0.5;
  constexpr std::uint64_t master_seed = 0x5C4E111971ull;
 
  Grid frame({side, side});
  seed_population(frame, 0xACE0u);
  const double initial = morans_i_binary(
    frame,
    static_cast<int>(Schelling_Cell::EMPTY),
    static_cast<int>(Schelling_Cell::TYPE_A),
    static_cast<int>(Schelling_Cell::TYPE_B));
 
  Schelling_Rule<> rule(threshold, /*p_move=*/0.7, /*p_fill=*/0.7, master_seed);
  Synchronous_Engine<Grid, Schelling_Rule<>, Moore<2, 1>> engine(std::move(frame), rule);
  engine.run(steps);
 
  const double final = morans_i_binary(
    engine.frame(),
    static_cast<int>(Schelling_Cell::EMPTY),
    static_cast<int>(Schelling_Cell::TYPE_A),
    static_cast<int>(Schelling_Cell::TYPE_B));
  const std::filesystem::path root = ALEPH_REPRODUCTIONS_SOURCE_DIR;
  std::filesystem::create_directories(root / "results");
  std::ofstream summary(root / "results" / "schelling_summary.csv");
  if (not summary)
    {
      std::cerr << "Cannot write Schelling summary\n";
      return 1;
    }
  summary << "side,steps,threshold,initial_morans_i,final_morans_i\n"
          << side << ',' << steps << ',' << threshold << ','
          << std::setprecision(12) << initial << ',' << final << '\n';
 
  std::cout << "Schelling segregation: initial Moran's I=" << std::fixed
            << std::setprecision(4) << initial << " final=" << final << '\n';
  if (final <= 0.7)
    {
      std::cerr << "Schelling final Moran's I must be greater than 0.7\n";
      return 2;
    }
  return 0;
}