# Setting solver limits

The following sections explain how to set limits on how long the solver searches for solutions.

## Setting a time limit for the solver

If your program takes a long time to run, we recommend setting a time limit for the solver, which ensures that the program will terminate in a reasonable length of time. The examples below illustrate how to set a limit of 10 seconds for the solver.

### Python

```"""Solves a problem with a time limit."""

from ortools.sat.python import cp_model

def solve_with_time_limit_sample_sat():
"""Minimal CP-SAT example to showcase calling the solver."""
# Creates the model.
model = cp_model.CpModel()
# Creates the variables.
num_vals = 3
x = model.new_int_var(0, num_vals - 1, "x")
y = model.new_int_var(0, num_vals - 1, "y")
z = model.new_int_var(0, num_vals - 1, "z")

# Creates a solver and solves the model.
solver = cp_model.CpSolver()

# Sets a time limit of 10 seconds.
solver.parameters.max_time_in_seconds = 10.0

status = solver.solve(model)

if status == cp_model.OPTIMAL:
print(f"x = {solver.value(x)}")
print(f"y = {solver.value(y)}")
print(f"z = {solver.value(z)}")

solve_with_time_limit_sample_sat()```

### C++

```#include <stdlib.h>

#include "ortools/base/logging.h"
#include "ortools/sat/cp_model.h"
#include "ortools/sat/cp_model.pb.h"
#include "ortools/sat/cp_model_solver.h"
#include "ortools/sat/model.h"
#include "ortools/sat/sat_parameters.pb.h"
#include "ortools/util/sorted_interval_list.h"

namespace operations_research {
namespace sat {

void SolveWithTimeLimitSampleSat() {
CpModelBuilder cp_model;

const Domain domain(0, 2);
const IntVar x = cp_model.NewIntVar(domain).WithName("x");
const IntVar y = cp_model.NewIntVar(domain).WithName("y");
const IntVar z = cp_model.NewIntVar(domain).WithName("z");

// Solving part.
Model model;

// Sets a time limit of 10 seconds.
SatParameters parameters;
parameters.set_max_time_in_seconds(10.0);

// Solve.
const CpSolverResponse response = SolveCpModel(cp_model.Build(), &model);
LOG(INFO) << CpSolverResponseStats(response);

if (response.status() == CpSolverStatus::OPTIMAL) {
LOG(INFO) << "  x = " << SolutionIntegerValue(response, x);
LOG(INFO) << "  y = " << SolutionIntegerValue(response, y);
LOG(INFO) << "  z = " << SolutionIntegerValue(response, z);
}
}

}  // namespace sat
}  // namespace operations_research

int main() {
operations_research::sat::SolveWithTimeLimitSampleSat();

return EXIT_SUCCESS;
}```

### Java

```package com.google.ortools.sat.samples;

/** Solves a problem with a time limit. */
public final class SolveWithTimeLimitSampleSat {
public static void main(String[] args) {
// Create the model.
CpModel model = new CpModel();
// Create the variables.
int numVals = 3;

IntVar x = model.newIntVar(0, numVals - 1, "x");
IntVar y = model.newIntVar(0, numVals - 1, "y");
IntVar z = model.newIntVar(0, numVals - 1, "z");
// Create the constraint.

// Create a solver and solve the model.
CpSolver solver = new CpSolver();
solver.getParameters().setMaxTimeInSeconds(10.0);
CpSolverStatus status = solver.solve(model);

if (status == CpSolverStatus.OPTIMAL) {
System.out.println("x = " + solver.value(x));
System.out.println("y = " + solver.value(y));
System.out.println("z = " + solver.value(z));
}
}

private SolveWithTimeLimitSampleSat() {}
}```

### C#

```using System;

public class SolveWithTimeLimitSampleSat
{
static void Main()
{
// Creates the model.
CpModel model = new CpModel();
// Creates the variables.
int num_vals = 3;

IntVar x = model.NewIntVar(0, num_vals - 1, "x");
IntVar y = model.NewIntVar(0, num_vals - 1, "y");
IntVar z = model.NewIntVar(0, num_vals - 1, "z");

// Creates a solver and solves the model.
CpSolver solver = new CpSolver();

// Adds a time limit. Parameters are stored as strings in the solver.
solver.StringParameters = "max_time_in_seconds:10.0";

CpSolverStatus status = solver.Solve(model);

if (status == CpSolverStatus.Optimal)
{
Console.WriteLine("x = " + solver.Value(x));
Console.WriteLine("y = " + solver.Value(y));
Console.WriteLine("z = " + solver.Value(z));
}
}
}```

## Stopping a search after a specified number of solutions

As an alternative to setting a time limit, you can make the solver terminate after it finds a specified number of solutions. The examples below illustrate how to stop the search after five solutions.

### Python

```"""Code sample that solves a model and displays a small number of solutions."""

from ortools.sat.python import cp_model

class VarArraySolutionPrinterWithLimit(cp_model.CpSolverSolutionCallback):
"""Print intermediate solutions."""

def __init__(self, variables: list[cp_model.IntVar], limit: int):
cp_model.CpSolverSolutionCallback.__init__(self)
self.__variables = variables
self.__solution_count = 0
self.__solution_limit = limit

def on_solution_callback(self) -> None:
self.__solution_count += 1
for v in self.__variables:
print(f"{v}={self.value(v)}", end=" ")
print()
if self.__solution_count >= self.__solution_limit:
print(f"Stop search after {self.__solution_limit} solutions")
self.stop_search()

@property
def solution_count(self) -> int:
return self.__solution_count

def stop_after_n_solutions_sample_sat():
"""Showcases calling the solver to search for small number of solutions."""
# Creates the model.
model = cp_model.CpModel()
# Creates the variables.
num_vals = 3
x = model.new_int_var(0, num_vals - 1, "x")
y = model.new_int_var(0, num_vals - 1, "y")
z = model.new_int_var(0, num_vals - 1, "z")

# Create a solver and solve.
solver = cp_model.CpSolver()
solution_printer = VarArraySolutionPrinterWithLimit([x, y, z], 5)
# Enumerate all solutions.
solver.parameters.enumerate_all_solutions = True
# Solve.
status = solver.solve(model, solution_printer)
print(f"Status = {solver.status_name(status)}")
print(f"Number of solutions found: {solution_printer.solution_count}")
assert solution_printer.solution_count == 5

stop_after_n_solutions_sample_sat()```

### C++

```#include <stdlib.h>

#include <atomic>

#include "ortools/base/logging.h"
#include "ortools/sat/cp_model.h"
#include "ortools/sat/cp_model.pb.h"
#include "ortools/sat/cp_model_solver.h"
#include "ortools/sat/model.h"
#include "ortools/sat/sat_parameters.pb.h"
#include "ortools/util/sorted_interval_list.h"
#include "ortools/util/time_limit.h"

namespace operations_research {
namespace sat {

void StopAfterNSolutionsSampleSat() {
CpModelBuilder cp_model;

const Domain domain(0, 2);
const IntVar x = cp_model.NewIntVar(domain).WithName("x");
const IntVar y = cp_model.NewIntVar(domain).WithName("y");
const IntVar z = cp_model.NewIntVar(domain).WithName("z");

Model model;

// Tell the solver to enumerate all solutions.
SatParameters parameters;
parameters.set_enumerate_all_solutions(true);

// Create an atomic Boolean that will be periodically checked by the limit.
std::atomic<bool> stopped(false);
model.GetOrCreate<TimeLimit>()->RegisterExternalBooleanAsLimit(&stopped);

const int kSolutionLimit = 5;
int num_solutions = 0;
LOG(INFO) << "Solution " << num_solutions;
LOG(INFO) << "  x = " << SolutionIntegerValue(r, x);
LOG(INFO) << "  y = " << SolutionIntegerValue(r, y);
LOG(INFO) << "  z = " << SolutionIntegerValue(r, z);
num_solutions++;
if (num_solutions >= kSolutionLimit) {
stopped = true;
LOG(INFO) << "Stop search after " << kSolutionLimit << " solutions.";
}
}));
const CpSolverResponse response = SolveCpModel(cp_model.Build(), &model);
LOG(INFO) << "Number of solutions found: " << num_solutions;
CHECK_EQ(num_solutions, kSolutionLimit);
}

}  // namespace sat
}  // namespace operations_research

int main() {
operations_research::sat::StopAfterNSolutionsSampleSat();

return EXIT_SUCCESS;
}```

### Java

```package com.google.ortools.sat.samples;

/** Code sample that solves a model and displays a small number of solutions. */
public final class StopAfterNSolutionsSampleSat {
static class VarArraySolutionPrinterWithLimit extends CpSolverSolutionCallback {
public VarArraySolutionPrinterWithLimit(IntVar[] variables, int limit) {
variableArray = variables;
solutionLimit = limit;
}

@Override
public void onSolutionCallback() {
System.out.printf("Solution #%d: time = %.02f s%n", solutionCount, wallTime());
for (IntVar v : variableArray) {
System.out.printf("  %s = %d%n", v.getName(), value(v));
}
solutionCount++;
if (solutionCount >= solutionLimit) {
System.out.printf("Stop search after %d solutions%n", solutionLimit);
stopSearch();
}
}

public int getSolutionCount() {
return solutionCount;
}

private int solutionCount;
private final IntVar[] variableArray;
private final int solutionLimit;
}

public static void main(String[] args) {
// Create the model.
CpModel model = new CpModel();
// Create the variables.
int numVals = 3;

IntVar x = model.newIntVar(0, numVals - 1, "x");
IntVar y = model.newIntVar(0, numVals - 1, "y");
IntVar z = model.newIntVar(0, numVals - 1, "z");

// Create a solver and solve the model.
CpSolver solver = new CpSolver();
VarArraySolutionPrinterWithLimit cb =
new VarArraySolutionPrinterWithLimit(new IntVar[] {x, y, z}, 5);
// Tell the solver to enumerate all solutions.
solver.getParameters().setEnumerateAllSolutions(true);
// And solve.
solver.solve(model, cb);

System.out.println(cb.getSolutionCount() + " solutions found.");
if (cb.getSolutionCount() != 5) {
throw new RuntimeException("Did not stop the search correctly.");
}
}

private StopAfterNSolutionsSampleSat() {}
}```

### C#

```using System;

public class VarArraySolutionPrinterWithLimit : CpSolverSolutionCallback
{
public VarArraySolutionPrinterWithLimit(IntVar[] variables, int solution_limit)
{
variables_ = variables;
solution_limit_ = solution_limit;
}

public override void OnSolutionCallback()
{
Console.WriteLine(String.Format("Solution #{0}: time = {1:F2} s", solution_count_, WallTime()));
foreach (IntVar v in variables_)
{
Console.WriteLine(String.Format("  {0} = {1}", v.ToString(), Value(v)));
}
solution_count_++;
if (solution_count_ >= solution_limit_)
{
Console.WriteLine(String.Format("Stopping search after {0} solutions", solution_limit_));
StopSearch();
}
}

public int SolutionCount()
{
return solution_count_;
}

private int solution_count_;
private IntVar[] variables_;
private int solution_limit_;
}

public class StopAfterNSolutionsSampleSat
{
static void Main()
{
// Creates the model.
CpModel model = new CpModel();
// Creates the variables.
int num_vals = 3;

IntVar x = model.NewIntVar(0, num_vals - 1, "x");
IntVar y = model.NewIntVar(0, num_vals - 1, "y");
IntVar z = model.NewIntVar(0, num_vals - 1, "z");

// Creates a solver and solves the model.
CpSolver solver = new CpSolver();
VarArraySolutionPrinterWithLimit cb = new VarArraySolutionPrinterWithLimit(new IntVar[] { x, y, z }, 5);
solver.StringParameters = "enumerate_all_solutions:true";
solver.Solve(model, cb);
Console.WriteLine(String.Format("Number of solutions found: {0}", cb.SolutionCount()));
}
}```
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{ "lastModified": "Last updated 2024-08-28 UTC.", "confidential": False }