fix: step-50 PETSc

add a missing include

diff --git a/examples/step-50/step-50.cc b/examples/step-50/step-50.cc
index c315c2dad5c54e2a8c78317ac7f5d37b19f9d13a..f07a70f08d64498c30907e94dce919c426ae50b5 100644 (file)
--- a/examples/step-50/step-50.cc
+++ b/examples/step-50/step-50.cc
@@ -43,6 +43,7 @@
 #include <deal.II/grid/tria.h>
 #include <deal.II/lac/affine_constraints.h>
 #include <deal.II/lac/dynamic_sparsity_pattern.h>
+#include <deal.II/lac/sparsity_tools.h>
 #include <deal.II/lac/solver_cg.h>
 
 // We use the same strategy as in step-40 to switch between PETSc and