From ce7b7b69457a1a262ba5571c02e482f743f18459 Mon Sep 17 00:00:00 2001
From: Sebastian Proell <sebastian.proell@tum.de>
Date: Sat, 13 May 2023 11:56:17 +0200
Subject: [PATCH] Fix step-77: zero out residual before assembly

---
 examples/step-77/step-77.cc | 2 ++
 tests/sundials/step-77.cc   | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/examples/step-77/step-77.cc b/examples/step-77/step-77.cc
index b58f350b20..ab75a26d72 100644
--- a/examples/step-77/step-77.cc
+++ b/examples/step-77/step-77.cc
@@ -334,6 +334,8 @@ namespace Step77
 
     std::cout << "  Computing residual vector..." << std::flush;
 
+    residual = 0.0;
+
     const QGauss<dim> quadrature_formula(fe.degree + 1);
     FEValues<dim>     fe_values(fe,
                             quadrature_formula,
diff --git a/tests/sundials/step-77.cc b/tests/sundials/step-77.cc
index 4c427d2636..d8aa4ffd28 100644
--- a/tests/sundials/step-77.cc
+++ b/tests/sundials/step-77.cc
@@ -243,6 +243,8 @@ namespace Step77
     const Vector<double> &evaluation_point,
     Vector<double> &      residual)
   {
+    residual = 0.0;
+
     const QGauss<dim> quadrature_formula(fe.degree + 1);
     FEValues<dim>     fe_values(fe,
                             quadrature_formula,
-- 
2.39.5