Joel, Yes the matrix you are assembling is a vector-valued mass matrix now. For me your code is failing with
void dealii::FEValuesBase<dim, spacedim>::get_function_gradients(const InputVector&, std::vector<dealii::Tensor<1, spacedim, typename InputVector::value_type> >&) const [with InputVector = dealii::Vector<double>; int dim = 3; int spacedim = 3; typename InputVector::value_type = double] The violated condition was: (fe->n_components()) == (1) The name and call sequence of the exception was: dealii::ExcDimensionMismatch((fe->n_components()),(1)) Additional Information: Dimension 3 not equal to 1 and this is not surprising. What you are doing is to extract the gradients of a vector-valued finite element solution. The object that should store this should therefore be a std::vector<std::vector<Tensor<1,dim>> as you want to store for each quadrature point and each component a Tensor<1,dim>. What you want to do is really that in "Do not work". As you have two DoFHandlers, you should also have two FEValues objects and two cell_iterator corresponding to the correct DoFHandler. Then you can extract the gradient of your scalar field and project it onto the ansatz space for the vector-valued field. This should look like: typename DoFHandler<dim>::active_cell_iterator cell_scalar = dof_handler_scalar.begin_active(); typename DoFHandler<dim>::active_cell_iterator cell = dof_handler.begin_active(); ... for (; cell!=endc; ++cell, ++cell_vector) { fe_values.reinit (cell); fe_values_scalar.reinit (cell_scalar); fe_values_scalar.get_function_gradients(test,fe_function_grad); ... } Best, Daniel -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.