From f80a49df09113e27f9c4144b2aea1dda4e3a5d66 Mon Sep 17 00:00:00 2001
From: Sebastian Proell <sebastian.proell@tum.de>
Date: Thu, 22 Sep 2022 16:38:31 +0200
Subject: [PATCH] Increase precision of time written in xdmf output

---
 source/base/data_out_base.cc                                | 1 +
 tests/data_out/data_out_hdf5_01.cc                          | 6 ++++--
 .../data_out_hdf5_01.with_hdf5=true.with_mpi=false.output   | 2 +-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/source/base/data_out_base.cc b/source/base/data_out_base.cc
index 99fc2c4e93..aceb6710ff 100644
--- a/source/base/data_out_base.cc
+++ b/source/base/data_out_base.cc
@@ -9783,6 +9783,7 @@ XDMFEntry::get_xdmf_content(const unsigned int indent_level) const
     return "";
 
   std::stringstream ss;
+  ss.precision(12);
   ss << indent(indent_level + 0)
      << "<Grid Name=\"mesh\" GridType=\"Uniform\">\n";
   ss << indent(indent_level + 1) << "<Time Value=\"" << entry_time << "\"/>\n";
diff --git a/tests/data_out/data_out_hdf5_01.cc b/tests/data_out/data_out_hdf5_01.cc
index 9e3f5d1909..14c5cfc53a 100644
--- a/tests/data_out/data_out_hdf5_01.cc
+++ b/tests/data_out/data_out_hdf5_01.cc
@@ -56,8 +56,10 @@ test()
   data_out.write_filtered_data(data_filter);
   data_out.write_hdf5_parallel(data_filter, "out.h5", MPI_COMM_SELF);
   std::vector<XDMFEntry> xdmf_entries;
-  xdmf_entries.push_back(
-    data_out.create_xdmf_entry(data_filter, "out.h5", 0, MPI_COMM_SELF));
+
+  // Use a point in time that requires high precision output
+  xdmf_entries.push_back(data_out.create_xdmf_entry(
+    data_filter, "out.h5", 1 + 1e-10, MPI_COMM_SELF));
 
   data_out.write_xdmf_file(xdmf_entries, "out.xdmf", MPI_COMM_SELF);
 
diff --git a/tests/data_out/data_out_hdf5_01.with_hdf5=true.with_mpi=false.output b/tests/data_out/data_out_hdf5_01.with_hdf5=true.with_mpi=false.output
index 911d9ff941..350a0ec1de 100644
--- a/tests/data_out/data_out_hdf5_01.with_hdf5=true.with_mpi=false.output
+++ b/tests/data_out/data_out_hdf5_01.with_hdf5=true.with_mpi=false.output
@@ -6,7 +6,7 @@ DEAL::ok
   <Domain>
     <Grid Name="CellTime" GridType="Collection" CollectionType="Temporal">
       <Grid Name="mesh" GridType="Uniform">
-        <Time Value="0"/>
+        <Time Value="1.0000000001"/>
         <Geometry GeometryType="XY">
           <DataItem Dimensions="36 2" NumberType="Float" Precision="8" Format="HDF">
             out.h5:/nodes
-- 
2.39.5