[Spring] Add empty buildStiffnessMatrix in JointSpringForceField

Author: hugtalbot

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*,

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*)
 {