From 271cf0324e92a3a874fed2233c96aae26736e31e Mon Sep 17 00:00:00 2001
From: Laurent Perron <lperron@google.com>
Date: Thu, 20 Jul 2023 15:36:45 -0700
Subject: [PATCH] [ModelBuilder] do not add term 0 * var

---
 ortools/linear_solver/python/model_builder_test.py     | 10 +++++-----
 ortools/linear_solver/wrappers/model_builder_helper.cc |  2 ++
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/ortools/linear_solver/python/model_builder_test.py b/ortools/linear_solver/python/model_builder_test.py
index 6f6b510579c..b473e108639 100644
--- a/ortools/linear_solver/python/model_builder_test.py
+++ b/ortools/linear_solver/python/model_builder_test.py
@@ -1034,7 +1034,7 @@ class ModelBuilderLinearConstraintsTest(parameterized.TestCase):
             constraint_count=1,
             lower_bounds=[-math.inf],
             upper_bounds=[0],
-            expression_terms=lambda x, y: [{x[0]: 0}],
+            expression_terms=lambda x, y: [{}],
             expression_offsets=[0],
         ),
         dict(
@@ -1064,7 +1064,7 @@ class ModelBuilderLinearConstraintsTest(parameterized.TestCase):
             constraint_count=1,
             lower_bounds=[0],
             upper_bounds=[math.inf],
-            expression_terms=lambda x, y: [{x[0]: 0}],
+            expression_terms=lambda x, y: [{}],
             expression_offsets=[0],
         ),
         dict(
@@ -1075,7 +1075,7 @@ class ModelBuilderLinearConstraintsTest(parameterized.TestCase):
             constraint_count=1,
             lower_bounds=[-math.inf],
             upper_bounds=[3],
-            expression_terms=lambda x, y: [{x[0]: 0}],
+            expression_terms=lambda x, y: [{}],
             expression_offsets=[0],
         ),
         dict(
@@ -1086,7 +1086,7 @@ class ModelBuilderLinearConstraintsTest(parameterized.TestCase):
             constraint_count=1,
             lower_bounds=[3],
             upper_bounds=[3],
-            expression_terms=lambda x, y: [{x[0]: 0}],
+            expression_terms=lambda x, y: [{}],
             expression_offsets=[0],
         ),
         dict(
@@ -1097,7 +1097,7 @@ class ModelBuilderLinearConstraintsTest(parameterized.TestCase):
             constraint_count=1,
             lower_bounds=[3],
             upper_bounds=[math.inf],
-            expression_terms=lambda x, y: [{x[0]: 0}],
+            expression_terms=lambda x, y: [{}],
             expression_offsets=[0],
         ),
         dict(
diff --git a/ortools/linear_solver/wrappers/model_builder_helper.cc b/ortools/linear_solver/wrappers/model_builder_helper.cc
index e3731363ac8..142a8523a58 100644
--- a/ortools/linear_solver/wrappers/model_builder_helper.cc
+++ b/ortools/linear_solver/wrappers/model_builder_helper.cc
@@ -142,6 +142,7 @@ void ModelBuilderHelper::SetConstraintUpperBound(int ct_index, double ub) {
 
 void ModelBuilderHelper::AddConstraintTerm(int ct_index, int var_index,
                                            double coeff) {
+  if (coeff == 0.0) return;
   MPConstraintProto* ct_proto = model_.mutable_constraint(ct_index);
   ct_proto->add_var_index(var_index);
   ct_proto->add_coefficient(coeff);
@@ -149,6 +150,7 @@ void ModelBuilderHelper::AddConstraintTerm(int ct_index, int var_index,
 
 void ModelBuilderHelper::SafeAddConstraintTerm(int ct_index, int var_index,
                                                double coeff) {
+  if (coeff == 0.0) return;
   MPConstraintProto* ct_proto = model_.mutable_constraint(ct_index);
   for (int i = 0; i < ct_proto->var_index_size(); ++i) {
     if (ct_proto->var_index(i) == var_index) {