From 14f409656fceab0fa10ebaffd3d3ad759aa0af98 Mon Sep 17 00:00:00 2001
From: hugtalbot <hugo.talbot@inria.fr>
Date: Tue, 27 Jan 2026 15:32:04 +0100
Subject: [PATCH] [Spring] Add empty buildStiffnessMatrix in
 JointSpringForceField

---
 .../solidmechanics/spring/JointSpringForceField.h          | 4 ++--
 .../solidmechanics/spring/JointSpringForceField.inl        | 7 +++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/JointSpringForceField.h b/Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/JointSpringForceField.h
index c3d0c4e2251..d927bd3adee 100644
--- a/Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/JointSpringForceField.h
+++ b/Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/JointSpringForceField.h
@@ -92,8 +92,6 @@ class JointSpringForceField : public core::behavior::PairInteractionForceField<D
     // project torsion to Lawfulltorsion according to limitangles
     void projectTorsion(Spring& spring);
 
-
-
     JointSpringForceField(MechanicalState* object1, MechanicalState* object2);
     JointSpringForceField();
 
@@ -123,6 +121,8 @@ class JointSpringForceField : public core::behavior::PairInteractionForceField<D
                            const DataVecDeriv& data_dx1,
                            const DataVecDeriv& data_dx2) override;
 
+    void buildStiffnessMatrix(core::behavior::StiffnessMatrix* matrix) override;
+
     void buildDampingMatrix(core::behavior::DampingMatrix* /*matrix*/) final;
 
     SReal getPotentialEnergy(const core::MechanicalParams*,
diff --git a/Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/JointSpringForceField.inl b/Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/JointSpringForceField.inl
index 615db18c398..4cf5b1cbea9 100644
--- a/Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/JointSpringForceField.inl
+++ b/Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/JointSpringForceField.inl
@@ -358,6 +358,13 @@ void JointSpringForceField<DataTypes>::addDForce(const core::MechanicalParams *m
     data_df2.endEdit();
 }
 
+template <class DataTypes>
+void JointSpringForceField<DataTypes>::buildStiffnessMatrix(core::behavior::StiffnessMatrix* matrix)
+{
+    SOFA_UNUSED(matrix);
+    msg_error() << "buildStiffnessMatrix not implemented (thus only computing explicit forces)";
+}
+
 template <class DataTypes>
 void JointSpringForceField<DataTypes>::buildDampingMatrix(core::behavior::DampingMatrix*)
 {