LinearExpr.sum

04_modelling.md

@@ -445,6 +445,19 @@ multiplying all terms by 3. However, this requires manual intervention, which
 undermines the idea of using a solver. These limitations are important to
 consider, although such scenarios are rare in practical applications.
 
+> [!TIP]
+>
+> If you have long sums of variables and coefficients, it can be more efficient to
+> use the sum-methods of LinearExpr than to use Python's sum-function. Note that
+> this function does currently not support generators.
+>
+> ```python
+> xs = [model.NewIntVar(0, 10, f"x{i}") for i in range(5)]
+> weights = [i for i in range(5)]
+> model.add(cp_model.LinearExpr.sum(xs) >= 1)
+> model.minimize(cp_model.LinearExpr.weighted_sum(xs, weights))
+> ```
+
 If you have a lower and an upper bound for a linear expression, you can also use
 the `add_linear_constraint`-method, which allows you to specify both bounds in
 one go.

tests/test_lin_constraints.py

@@ -20,6 +20,15 @@ def test_lin_constraints():
     model.add(x < y + z)
     model.add(y > 300 - 4 * z)
 
+def test_lin_constraint_sum():
+    model = cp_model.CpModel()
+    vars = [model.NewIntVar(0, 10, f"x{i}") for i in range(5)]
+    weights = [i for i in range(5)]
+    model.add(cp_model.LinearExpr.sum(vars) >= 1)
+    model.minimize(cp_model.LinearExpr.weighted_sum(vars, weights))
+
+
+
 
 def test_infeasible_intersection():
     model = cp_model.CpModel()