From: Julian Roth <mathmerizing@gmail.com>
Date: Mon, 25 May 2020 14:51:05 +0000 (+0200)
Subject: Added nullptr check before applying user constraints to transfer matrices.
X-Git-Tag: v9.3.0-rc1~1476^2~4
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5b20c525754ab98f7225f31922033edfbb57c742;p=dealii.git

Added nullptr check before applying user constraints to transfer matrices.
---

diff --git a/doc/news/changes/minor/20200525Roth b/doc/news/changes/minor/20200525Roth
new file mode 100644
index 0000000000..cfeef832e7
--- /dev/null
+++ b/doc/news/changes/minor/20200525Roth
@@ -0,0 +1,4 @@
+New: Applying user constraints 
+after prolongation and restriction in MGTransferPrebuilt.
+<br>
+(Julian Roth, 2020/05/25)
diff --git a/source/multigrid/mg_transfer_prebuilt.cc b/source/multigrid/mg_transfer_prebuilt.cc
index 99130d4c94..7295d243b1 100644
--- a/source/multigrid/mg_transfer_prebuilt.cc
+++ b/source/multigrid/mg_transfer_prebuilt.cc
@@ -86,8 +86,9 @@ MGTransferPrebuilt<VectorType>::prolongate(const unsigned int to_level,
          ExcIndexRange(to_level, 1, prolongation_matrices.size() + 1));
 
   prolongation_matrices[to_level - 1]->vmult(dst, src);
-  this->mg_constrained_dofs->get_user_constraint_matrix(to_level).distribute(
-    dst);
+  if (this->mg_constrained_dofs != nullptr)
+    this->mg_constrained_dofs->get_user_constraint_matrix(to_level).distribute(
+      dst);
 }
 
 
@@ -103,8 +104,9 @@ MGTransferPrebuilt<VectorType>::restrict_and_add(const unsigned int from_level,
   (void)from_level;
 
   prolongation_matrices[from_level - 1]->Tvmult_add(dst, src);
-  this->mg_constrained_dofs->get_user_constraint_matrix(from_level - 1)
-    .distribute(dst);
+  if (this->mg_constrained_dofs != nullptr)
+    this->mg_constrained_dofs->get_user_constraint_matrix(from_level - 1)
+      .distribute(dst);
 }