set hotstart false by default and restore zero-ing forces if cold start

Author: fredroy

Sofa/Component/Constraint/Lagrangian/Solver/src/sofa/component/constraint/lagrangian/solver/UnbuiltConstraintSolver.cpp

@@ -31,7 +31,7 @@ namespace sofa::component::constraint::lagrangian::solver
 
 UnbuiltConstraintSolver::UnbuiltConstraintSolver()
 : GenericConstraintSolver()
-, d_initialGuess(initData(&d_initialGuess, true, "initialGuess", "Activate constraint force history to improve convergence (hot start)"))
+, d_initialGuess(initData(&d_initialGuess, false, "initialGuess", "Activate constraint force history to possibly improve convergence (hot start)."))
 {
 
 }
@@ -69,11 +69,9 @@ void UnbuiltConstraintSolver::doBuildSystem( const core::ConstraintParams *cPara
     for (unsigned int i = 0; i < numConstraints; i++)
         c_current_cp->cclist_elems[i].resize(nbCC, nullptr);
 
-    unsigned int nbObjects = 0;
     for (unsigned int c_id = 0; c_id < numConstraints;)
     {
         bool foundCC = false;
-        nbObjects++;
         const unsigned int l = c_current_cp->constraintsResolutions[c_id]->getNbLines();
 
         for (unsigned int j = 0; j < l_constraintCorrections.size(); j++)
@@ -153,7 +151,7 @@ void UnbuiltConstraintSolver::computeInitialGuess()
     {
         force[c] = 0.0;
     }
-
+    
     // Then restore forces from previous timestep for matching persistent IDs
     for (const ConstraintBlockInfo& info : m_constraintBlockInfo)
     {

Sofa/Component/Constraint/Lagrangian/Solver/src/sofa/component/constraint/lagrangian/solver/UnbuiltGaussSeidelConstraintSolver.cpp

@@ -77,16 +77,20 @@ void UnbuiltGaussSeidelConstraintSolver::doSolve(GenericConstraintProblem * prob
     {
         if(!c_current_cp->constraintsResolutions[i])
         {
-            msg_warning() << "Bad size of constraintsResolutions in GenericConstraintSolver" ;
+            msg_warning() << "Bad size of constraintsResolutions" ;
             c_current_cp->setDimension(i);
             break;
         }
         c_current_cp->constraintsResolutions[i]->init(i, w, force);
         i += c_current_cp->constraintsResolutions[i]->getNbLines();
     }
-    // Note: force array is now initialized by GenericConstraintSolver::computeInitialGuess()
-    // for hot-start support. Do not zero forces here.
 
+    // zero forces if cold-start
+    if(!d_initialGuess.getValue())
+    {
+        memset(force, 0, c_current_cp->getDimension() * sizeof(SReal));
+    }
+    
     bool showGraphs = false;
     sofa::type::vector<SReal>* graph_residuals = nullptr;
     std::map < std::string, sofa::type::vector<SReal> > *graph_forces = nullptr, *graph_violations = nullptr;