r9757/sofa : ForceField: added helper to build a sparse Eigen stiffness matrix
r9757/sofa : ForceField: added helper to build a sparse Eigen stiffness matrix


Former-commit-id: d1fa5d65627a0a956a05272ddb27918c923e72d1
hdeling/sofa,FabienPean/sofa,FabienPean/sofa,Anatoscope/sofa,FabienPean/sofa,Anatoscope/sofa,Anatoscope/sofa,Anatoscope/sofa,FabienPean/sofa,FabienPean/sofa,hdeling/sofa,Anatoscope/sofa,FabienPean/sofa,hdeling/sofa,FabienPean/sofa,hdeling/sofa,Anatoscope/sofa,FabienPean/sofa,hdeling/sofa,hdeling/sofa,hdeling/sofa,FabienPean/sofa,Anatoscope/sofa,hdeling/sofa,FabienPean/sofa,hdeling/sofa,Anatoscope/sofa,Anatoscope/sofa,hdeling/sofa