Add write_diagonstics_on_restart input option (#4091)

* Add write_diagonstics_on_restart input option

* Add doc to new variable

Co-authored-by: Axel Huebl <axel.huebl@plasma.ninja>

* Use correct time step

---------

Co-authored-by: Axel Huebl <axel.huebl@plasma.ninja>

3 files changed, 10 insertions, 3 deletions

diff --git a/Source/Initialization/WarpXInitData.cpp b/Source/Initialization/WarpXInitData.cpp
index 0e1bb4aa7..233d03a0c 100644
--- a/Source/Initialization/WarpXInitData.cpp
+++ b/Source/Initialization/WarpXInitData.cpp
@@ -483,15 +483,17 @@ WarpX::InitData ()
         // looks at field values will see the composite of the field
         // solution and any external field
         AddExternalFields();
+    }
 
+    if (restart_chkfile.empty() || write_diagonstics_on_restart) {
         // Write full diagnostics before the first iteration.
-        multi_diags->FilterComputePackFlush( -1 );
+        multi_diags->FilterComputePackFlush(istep[0] - 1);
 
         // Write reduced diagnostics before the first iteration.
         if (reduced_diags->m_plot_rd != 0)
         {
-            reduced_diags->ComputeDiags(-1);
-            reduced_diags->WriteToFile(-1);
+            reduced_diags->ComputeDiags(istep[0] - 1);
+            reduced_diags->WriteToFile(istep[0] - 1);
         }
     }
 
diff --git a/Source/WarpX.H b/Source/WarpX.H
index eeb71f042..3a740d1b0 100644
--- a/Source/WarpX.H
+++ b/Source/WarpX.H
@@ -1540,6 +1540,9 @@ private:
 
     std::string restart_chkfile;
 
+    /** When `true`, write the diagnostics after restart at the time of the restart. */
+    bool write_diagonstics_on_restart = false;
+
     amrex::VisMF::Header::Version plotfile_headerversion  = amrex::VisMF::Header::Version_v1;
     amrex::VisMF::Header::Version slice_plotfile_headerversion  = amrex::VisMF::Header::Version_v1;
 
diff --git a/Source/WarpX.cpp b/Source/WarpX.cpp
index 8d4e98462..27d463c12 100644
--- a/Source/WarpX.cpp
+++ b/Source/WarpX.cpp
@@ -617,6 +617,8 @@ WarpX::ReadParameters ()
             }
         }
 
+        pp_warpx.query("write_diagonstics_on_restart", write_diagonstics_on_restart);
+
         pp_warpx.queryarr("checkpoint_signals", signals_in);
 #if defined(__linux__) || defined(__APPLE__)
         for (const std::string &str : signals_in) {