Merge pull request #16967 from tjhei/step-77-constraints

step-77: use AffineConstraints only

diff --cc examples/step-77/step-77.cc
index a279deddcf6b60c946f807188ecb76b3f3f68db2,30fc66af84adfee0e2ffadab108de4b720a8125e..4ca1c811f350a8a303e1fde14f33129240be166c
--- 1/examples/step-77/step-77.cc
--- 2/examples/step-77/step-77.cc
+++ b/examples/step-77/step-77.cc
@@@ -109,9 -108,10 +108,10 @@@ namespace Step7
      Triangulation<dim> triangulation;
  
      DoFHandler<dim> dof_handler;
 -    FE_Q<dim>       fe;
 +    const FE_Q<dim> fe;
  
-     AffineConstraints<double> hanging_node_constraints;
+     AffineConstraints<double> zero_constraints;
+     AffineConstraints<double> nonzero_constraints;
  
      SparsityPattern                      sparsity_pattern;
      SparseMatrix<double>                 jacobian_matrix;