% Décompte des masses
for i = 1:3
    ndof = (n_mass-1)*n_dof+i;
    M(ndof,ndof) = M(ndof,ndof) + Mu;
    ndof = (n_act-1)*n_dof+i;
    M(ndof,ndof) = M(ndof,ndof) + Ma;
end

% ------ Liste des masses -----------------------------------------------
for i = 1:n_nodes
  Mass(i) = M((i-1)*n_dof+3, (i-1)*n_dof+3);
end
Masses_FEM = [ [1:n_nodes]' Mass' ]