LocalToGlobalIndexMap::RowColumnIndices
LocalToGlobalIndexMap::operator[](std::size_t const mesh_item_id) const
{
    return RowColumnIndices(_rows[mesh_item_id], _columns[mesh_item_id]);
}
LocalToGlobalIndexMap::RowColumnIndices LocalToGlobalIndexMap::operator()(
    std::size_t const mesh_item_id, const int component_id) const
{
    return RowColumnIndices(_rows(mesh_item_id, component_id),
                            _columns(mesh_item_id, component_id));
}