def main():
# Create the linear solver with the GLOP backend.
solver = Solver('simple_lp_program', Solver.GLOP_LINEAR_PROGRAMMING)
# Create the variables x and y.
x = solver.NumVar(0, 1, 'x')
y = solver.NumVar(0, 2, 'y')
print('Number of variables =', solver.NumVariables())
# Create a linear constraint, 0 <= x + y <= 2.
ct = solver.Constraint(0, 2, 'ct')
ct.SetCoefficient(x, 1)
ct.SetCoefficient(y, 1)
print('Number of constraints =', solver.NumConstraints())
# Create the objective function, 3 * x + y.
objective = solver.Objective()
objective.SetCoefficient(x, 3)
objective.SetCoefficient(y, 1)
objective.SetMaximization()
solver.Solve()
print('Solution:')
print('Objective value =', objective.Value())
print('x =', x.solution_value())
print('y =', y.solution_value())
def _parse_constraint(solver: pywraplp.Solver, core_line: str, line_nr: int,
var_names: set):
# We don't care about the coefficient name before the colon
constraint_part = core_line
spl_colon = core_line.split(":", maxsplit=1)
if len(spl_colon) > 1:
constraint_part = spl_colon[1].strip()
# Equality constraint
if constraint_part.find("=") >= 0 and constraint_part.find(
"<=") == -1 and constraint_part.find(">=") == -1:
equality_spl = constraint_part.split("=")
if len(equality_spl) > 2:
raise ValueError(
"Equality constraint on line %d has multiple equal signs." %
line_nr)
if not _is_valid_constant_float(equality_spl[1]):
raise ValueError(
"Right hand side (\"%s\") of equality constraint on line %d is not a float "
"(e.g., variables are not allowed there!)." %
(equality_spl[1], line_nr))
equal_value = float(equality_spl[1])
constraint = solver.Constraint(equal_value, equal_value)
constant = _set_coefficients(solver, constraint, equality_spl[0],
line_nr, var_names)
constraint.SetLb(constraint.Lb() - constant)
constraint.SetUb(constraint.Ub() - constant)
_attempt_to_improve_var_bounds_two_hs(solver, equality_spl[0], True,
equality_spl[1], equality_spl[1])
# Inequality constraints
else:
# Replace all of these inequality signs, because they are equivalent
constraint_part = constraint_part.replace("<=", "<").replace(">=", ">")
# lower bound < ... < upper bound
if constraint_part.count("<") == 2:
spl = constraint_part.split("<")
if not _is_valid_constant_float(spl[0]):
raise ValueError(
"Left hand side (\"%s\") of inequality constraint on line %d is not a float "
"(e.g., variables are not allowed there!)." %
(spl[0], line_nr))
if not _is_valid_constant_float(spl[2]):
raise ValueError(
"Right hand side (\"%s\") of inequality constraint on line %d is not a float "
"(e.g., variables are not allowed there!)." %
(spl[2], line_nr))
constraint = solver.Constraint(float(spl[0]), float(spl[2]))
constant = _set_coefficients(solver, constraint, spl[1], line_nr,
var_names)
constraint.SetLb(constraint.Lb() - constant)
constraint.SetUb(constraint.Ub() - constant)
_attempt_to_improve_var_bounds_two_hs(solver, spl[1], True, spl[0],
spl[2])
# upper bound > ... > lower bound
elif constraint_part.count(">") == 2:
spl = constraint_part.split(">")
if not _is_valid_constant_float(spl[0]):
raise ValueError(
"Left hand side (\"%s\") of inequality constraint on line %d is not a float "
"(e.g., variables are not allowed there!)." %
(spl[0], line_nr))
if not _is_valid_constant_float(spl[2]):
raise ValueError(
"Right hand side (\"%s\") of inequality constraint on line %d is not a float "
"(e.g., variables are not allowed there!)." %
(spl[2], line_nr))
constraint = solver.Constraint(float(spl[2]), float(spl[0]))
constant = _set_coefficients(solver, constraint, spl[1], line_nr,
var_names)
constraint.SetLb(constraint.Lb() - constant)
constraint.SetUb(constraint.Ub() - constant)
_attempt_to_improve_var_bounds_two_hs(solver, spl[1], False,
spl[0], spl[2])
# ... < upper bound
elif constraint_part.count("<") == 1:
spl = constraint_part.split("<")
if not _is_valid_constant_float(spl[1]):
raise ValueError(
"Right hand side (\"%s\") of inequality constraint on line %d is not a float "
"(e.g., variables are not allowed there!)." %
(spl[1], line_nr))
constraint = solver.Constraint(-solver.infinity(), float(spl[1]))
constant = _set_coefficients(solver, constraint, spl[0], line_nr,
var_names)
constraint.SetUb(constraint.Ub() - constant)
_attempt_to_improve_var_bounds_one_hs(solver, spl[0], True, spl[1])
# ... > lower bound
elif constraint_part.count(">") == 1:
spl = constraint_part.split(">")
if not _is_valid_constant_float(spl[1]):
raise ValueError(
"Right hand side (\"%s\") of inequality constraint on line %d is not a float "
"(e.g., variables are not allowed there!)." %
(spl[1], line_nr))
constraint = solver.Constraint(float(spl[1]), solver.infinity())
constant = _set_coefficients(solver, constraint, spl[0], line_nr,
var_names)
constraint.SetLb(constraint.Lb() - constant)
_attempt_to_improve_var_bounds_one_hs(solver, spl[0], False,
spl[1])
# ...
elif constraint_part.count(">") == 0 and constraint_part.count(
"<") == 0:
raise ValueError(
"No (in)equality sign present for constraint on line %d." %
line_nr)
# Some strange combination
else:
raise ValueError(
"Too many (in)equality signs present for constraint on line %d."
% line_nr)
