cp_sat_example.py

#!/usr/bin/env python3
# Copyright 2010-2021 Google LLC
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# [START program]
"""Simple solve."""
# [START import]
from ortools.sat.python import cp_model
# [END import]


def main():
    """Minimal CP-SAT example to showcase calling the solver."""
    # Creates the model.
    # [START model]
    model = cp_model.CpModel()
    # [END model]

    # Creates the variables.
    # [START variables]
    var_upper_bound = max(50, 45, 37)
    x = model.NewIntVar(0, var_upper_bound, 'x')
    y = model.NewIntVar(0, var_upper_bound, 'y')
    z = model.NewIntVar(0, var_upper_bound, 'z')
    # [END variables]

    # Creates the constraints.
    # [START constraints]
    model.Add(2 * x + 7 * y + 3 * z <= 50)
    model.Add(3 * x - 5 * y + 7 * z <= 45)
    model.Add(5 * x + 2 * y - 6 * z <= 37)
    # [END constraints]

    # [START objective]
    model.Maximize(2 * x + 2 * y + 3 * z)
    # [END objective]

    # Creates a solver and solves the model.
    # [START solve]
    solver = cp_model.CpSolver()
    status = solver.Solve(model)
    # [END solve]

    # [START print_solution]
    if status == cp_model.OPTIMAL or status == cp_model.FEASIBLE:
        print(f'Maximum of objective function: {solver.ObjectiveValue()}\n')
        print(f'x = {solver.Value(x)}')
        print(f'y = {solver.Value(y)}')
        print(f'z = {solver.Value(z)}')
    else:
        print('No solution found.')
    # [END print_solution]

    # Statistics.
    # [START statistics]
    print('\nStatistics')
    print(f'  status   : {solver.StatusName(status)}')
    print(f'  conflicts: {solver.NumConflicts()}')
    print(f'  branches : {solver.NumBranches()}')
    print(f'  wall time: {solver.WallTime()} s')
    # [END statistics]


if __name__ == '__main__':
    main()
# [END program]