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Allow zero-valued LP Python model updates #1421

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14 changes: 9 additions & 5 deletions python/cuopt/cuopt/linear_programming/problem.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1726,7 +1726,7 @@ def addConstraint(self, constr, name=""):
raise ValueError("addConstraint requires a Constraint object")
return constr

def updateConstraint(self, constr, coeffs=[], rhs=None):
def updateConstraint(self, constr, coeffs=None, rhs=None):
"""
Updates a previously added constraint. Values that can be updated are
constraint coefficients and RHS.
Expand All @@ -1751,6 +1751,8 @@ def updateConstraint(self, constr, coeffs=[], rhs=None):
>>> problem.updateConstraint(c1, coeffs=[(x, 1)], rhs=10)
"""
self.reset_solved_values()
if coeffs is None:
coeffs = []
if isinstance(constr, Constraint):
if constr.is_quadratic:
raise ValueError(
Expand All @@ -1761,7 +1763,7 @@ def updateConstraint(self, constr, coeffs=[], rhs=None):
for var, coeff in coeffs:
idx = var.index
constr.vindex_coeff_dict[idx] = coeff
if rhs:
if rhs is not None:
constr.RHS = rhs
else:
raise ValueError("Object to update must be a Constraint")
Expand Down Expand Up @@ -1840,7 +1842,7 @@ def setObjective(self, expr, sense=MINIMIZE):
"Objective must be a Variable, Expression or a constant"
)

def updateObjective(self, coeffs=[], constant=None, sense=None):
def updateObjective(self, coeffs=None, constant=None, sense=None):
"""
Updates the objective of the problem. Values that can be updated are
objective coefficients, constant and sense.
Expand All @@ -1865,13 +1867,15 @@ def updateObjective(self, coeffs=[], constant=None, sense=None):
sense=MINIMIZE)
"""
self.reset_solved_values()
if coeffs is None:
coeffs = []
if isinstance(coeffs, dict):
coeffs = coeffs.items()
for var, coeff in coeffs:
var.setObjectiveCoefficient(coeff)
if constant:
if constant is not None:
self.ObjConstant = constant
if sense:
if sense is not None:
self.ObjSense = sense

def getIncumbentValues(self, solution, vars):
Expand Down
16 changes: 16 additions & 0 deletions python/cuopt/cuopt/tests/linear_programming/test_python_API.py
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Original file line number Diff line number Diff line change
Expand Up @@ -566,6 +566,22 @@ def test_problem_update():
assert prob.ObjValue == pytest.approx(5)


def test_problem_update_accepts_zero_values():
prob = Problem()
x = prob.addVariable(vtype=INTEGER, lb=0, name="x")
c1 = prob.addConstraint(x <= 5, name="c1")

prob.updateConstraint(c1, rhs=0)

assert c1.RHS == 0

prob.setObjective(x + 5)

prob.updateObjective(constant=0)

assert prob.ObjConstant == 0


def test_quadratic_expression_and_matrix():
problem = Problem()
x = problem.addVariable(lb=9.0, vtype="I", name="x")
Expand Down