ortools-clone/ortools/constraint_solver/docs/CP.md

Using the CP solver

https://developers.google.com/optimization/cp/

Documentation structure

OR-Tools comes with lots of constraint programming samples given in C++, Python, Java and .Net. Each language have different requirements for the code samples.

Basic example

C++ code samples

// Snippet from ortools/constraint_solver/samples/simple_cp_program.cc
#include <ostream>
#include <string>

#include "ortools/base/init_google.h"
#include "absl/base/log_severity.h"
#include "absl/log/globals.h"
#include "ortools/constraint_solver/constraint_solver.h"

namespace operations_research {

void SimpleCpProgram() {
  // Instantiate the solver.
  Solver solver("CpSimple");

  // Create the variables.
  const int64_t num_vals = 3;
  IntVar* const x = solver.MakeIntVar(0, num_vals - 1, "x");
  IntVar* const y = solver.MakeIntVar(0, num_vals - 1, "y");
  IntVar* const z = solver.MakeIntVar(0, num_vals - 1, "z");

  // Constraint 0: x != y..
  solver.AddConstraint(solver.MakeAllDifferent({x, y}));
  LOG(INFO) << "Number of constraints: "
            << std::to_string(solver.constraints());

  // Solve the problem.
  DecisionBuilder* const db = solver.MakePhase(
      {x, y, z}, Solver::CHOOSE_FIRST_UNBOUND, Solver::ASSIGN_MIN_VALUE);

  // Print solution on console.
  int count = 0;
  solver.NewSearch(db);
  while (solver.NextSolution()) {
    ++count;
    LOG(INFO) << "Solution " << count << ":" << std::endl
              << " x=" << x->Value() << " y=" << y->Value()
              << " z=" << z->Value();
  }
  solver.EndSearch();
  LOG(INFO) << "Number of solutions found: " << solver.solutions();

  LOG(INFO) << "Advanced usage:" << std::endl
            << "Problem solved in " << std::to_string(solver.wall_time())
            << "ms" << std::endl
            << "Memory usage: " << std::to_string(Solver::MemoryUsage())
            << "bytes";
}

}  // namespace operations_research

int main(int argc, char* argv[]) {
  InitGoogle(argv[0], &argc, &argv, true);
  absl::SetStderrThreshold(absl::LogSeverityAtLeast::kInfo);
  operations_research::SimpleCpProgram();
  return EXIT_SUCCESS;
}

Python code samples

# Snippet from ortools/constraint_solver/samples/simple_cp_program.py
"""Simple Constraint optimization example."""

from ortools.constraint_solver import pywrapcp


def main():
  """Entry point of the program."""
  # Instantiate the solver.
  solver = pywrapcp.Solver("CPSimple")

  # Create the variables.
  num_vals = 3
  x = solver.IntVar(0, num_vals - 1, "x")
  y = solver.IntVar(0, num_vals - 1, "y")
  z = solver.IntVar(0, num_vals - 1, "z")

  # Constraint 0: x != y.
  solver.Add(x != y)
  print("Number of constraints: ", solver.Constraints())

  # Solve the problem.
  decision_builder = solver.Phase(
      [x, y, z], solver.CHOOSE_FIRST_UNBOUND, solver.ASSIGN_MIN_VALUE
  )

  # Print solution on console.
  count = 0
  solver.NewSearch(decision_builder)
  while solver.NextSolution():
    count += 1
    solution = f"Solution {count}:\n"
    for var in [x, y, z]:
      solution += f" {var.Name()} = {var.Value()}"
    print(solution)
  solver.EndSearch()
  print(f"Number of solutions found: {count}")

  print("Advanced usage:")
  print(f"Problem solved in {solver.WallTime()}ms")
  print(f"Memory usage: {pywrapcp.Solver.MemoryUsage()}bytes")


if __name__ == "__main__":
  main()

Java code samples

// Snippet from ortools/constraint_solver/samples/SimpleCpProgram.java
package com.google.ortools.constraintsolver.samples;
import com.google.ortools.Loader;
import com.google.ortools.constraintsolver.DecisionBuilder;
import com.google.ortools.constraintsolver.IntVar;
import com.google.ortools.constraintsolver.Solver;
import java.util.logging.Logger;

/** Simple CP Program.*/
public class SimpleCpProgram {
  private SimpleCpProgram() {}

  private static final Logger logger = Logger.getLogger(SimpleCpProgram.class.getName());

  public static void main(String[] args) throws Exception {
    Loader.loadNativeLibraries();
    // Instantiate the solver.
    Solver solver = new Solver("CpSimple");

    // Create the variables.
    final long numVals = 3;
    final IntVar x = solver.makeIntVar(0, numVals - 1, "x");
    final IntVar y = solver.makeIntVar(0, numVals - 1, "y");
    final IntVar z = solver.makeIntVar(0, numVals - 1, "z");

    // Constraint 0: x != y..
    solver.addConstraint(solver.makeAllDifferent(new IntVar[]{x, y}));
    logger.info("Number of constraints: " + solver.constraints());

    // Solve the problem.
    final DecisionBuilder db = solver.makePhase(
        new IntVar[]{x, y, z},
        Solver.CHOOSE_FIRST_UNBOUND,
        Solver.ASSIGN_MIN_VALUE);

    // Print solution on console.
    int count = 0;
    solver.newSearch(db);
    while (solver.nextSolution()) {
      ++count;
      logger.info(String.format("Solution: %d\n x=%d y=%d z=%d"
          , count
          , x.value()
          , y.value()
          , z.value()));
    }
    solver.endSearch();
    logger.info("Number of solutions found: " + solver.solutions());

    logger.info(String.format(
          "Advanced usage:\nProblem solved in %d ms\nMemory usage: %d bytes"
          , solver.wallTime(), Solver.memoryUsage()));
  }
}

.Net code samples

// Snippet from ortools/constraint_solver/samples/SimpleCpProgram.cs
using System;
using Google.OrTools.ConstraintSolver;

/// <summary>
///   This is a simple CP program.
/// </summary>
public class SimpleCpProgram {
  public static void Main(String[] args) {
    // Instantiate the solver.
    Solver solver = new Solver("CpSimple");

    // Create the variables.
    const long numVals = 3;
    IntVar x = solver.MakeIntVar(0, numVals - 1, "x");
    IntVar y = solver.MakeIntVar(0, numVals - 1, "y");
    IntVar z = solver.MakeIntVar(0, numVals - 1, "z");

    // Constraint 0: x != y..
    solver.Add(solver.MakeAllDifferent(new IntVar[] { x, y }));
    Console.WriteLine($"Number of constraints: {solver.Constraints()}");

    // Solve the problem.
    DecisionBuilder db = solver.MakePhase(new IntVar[] { x, y, z }, Solver.CHOOSE_FIRST_UNBOUND,
                                          Solver.ASSIGN_MIN_VALUE);

    // Print solution on console.
    int count = 0;
    solver.NewSearch(db);
    while (solver.NextSolution()) {
      ++count;
      Console.WriteLine($"Solution: {count}\n x={x.Value()} y={y.Value()} z={z.Value()}");
    }
    solver.EndSearch();
    Console.WriteLine($"Number of solutions found: {solver.Solutions()}");

    Console.WriteLine("Advanced usage:");
    Console.WriteLine($"Problem solved in {solver.WallTime()}ms");
    Console.WriteLine($"Memory usage: {Solver.MemoryUsage()}bytes");
  }
}