From 2f3c73217b0a78e23f843a984cbb6f67d02f8993 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Tue, 15 Sep 2020 10:50:44 -0400
Subject: [PATCH] detect if dt has been changed from default and print warning
 if reset by units command

---
 src/USER-EFF/pair_eff_cut.cpp      |  2 +-
 src/USER-SMD/fix_smd_adjust_dt.cpp |  1 +
 src/fix_dt_reset.cpp               |  1 +
 src/input.cpp                      |  1 +
 src/update.cpp                     | 31 ++++++++++++++++++++++--------
 src/update.h                       |  1 +
 6 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/src/USER-EFF/pair_eff_cut.cpp b/src/USER-EFF/pair_eff_cut.cpp
index f4e7af6584..72281c4a50 100644
--- a/src/USER-EFF/pair_eff_cut.cpp
+++ b/src/USER-EFF/pair_eff_cut.cpp
@@ -869,7 +869,7 @@ void PairEffCut::init_style()
   // make sure to use the appropriate timestep when using real units
 
   if (update->whichflag == 1) {
-    if (force->qqr2e == 332.06371 && update->dt == 1.0)
+    if (utils::strmatch(update->unit_style,"^real") && update->dt_default)
       error->all(FLERR,"Must lower the default real units timestep for pEFF ");
   }
 
diff --git a/src/USER-SMD/fix_smd_adjust_dt.cpp b/src/USER-SMD/fix_smd_adjust_dt.cpp
index b5dab3d3a1..2acf6bd3ec 100644
--- a/src/USER-SMD/fix_smd_adjust_dt.cpp
+++ b/src/USER-SMD/fix_smd_adjust_dt.cpp
@@ -186,6 +186,7 @@ void FixSMDTlsphDtReset::end_of_step() {
 
 
         update->dt = dt;
+        update->dt_default = 0;
         if (force->pair)
                 force->pair->reset_dt();
         for (int i = 0; i < modify->nfix; i++)
diff --git a/src/fix_dt_reset.cpp b/src/fix_dt_reset.cpp
index 360f0d2998..4a9465e696 100644
--- a/src/fix_dt_reset.cpp
+++ b/src/fix_dt_reset.cpp
@@ -190,6 +190,7 @@ void FixDtReset::end_of_step()
 
   update->update_time();
   update->dt = dt;
+  update->dt_default = 0;
   if (respaflag) update->integrate->reset_dt();
   if (force->pair) force->pair->reset_dt();
   for (int i = 0; i < modify->nfix; i++) modify->fix[i]->reset_dt();
diff --git a/src/input.cpp b/src/input.cpp
index 6456f6c229..3a136cd44b 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -1871,6 +1871,7 @@ void Input::timestep()
 {
   if (narg != 1) error->all(FLERR,"Illegal timestep command");
   update->dt = utils::numeric(FLERR,arg[0],false,lmp);
+  update->dt_default = 0;
 }
 
 /* ---------------------------------------------------------------------- */
diff --git a/src/update.cpp b/src/update.cpp
index 399584473c..d591e05131 100644
--- a/src/update.cpp
+++ b/src/update.cpp
@@ -12,18 +12,22 @@
 ------------------------------------------------------------------------- */
 
 #include "update.h"
-#include <cstring>
-#include "integrate.h"
-#include "min.h"
+
 #include "style_integrate.h"  // IWYU pragma: keep
 #include "style_minimize.h"   // IWYU pragma: keep
-#include "neighbor.h"
-#include "force.h"
-#include "modify.h"
-#include "fix.h"
+
+#include "comm.h"
 #include "compute.h"
-#include "output.h"
+#include "integrate.h"
 #include "error.h"
+#include "fix.h"
+#include "force.h"
+#include "min.h"
+#include "modify.h"
+#include "neighbor.h"
+#include "output.h"
+
+#include <cstring>
 
 using namespace LAMMPS_NS;
 
@@ -48,6 +52,7 @@ Update::Update(LAMMPS *lmp) : Pointers(lmp)
 
   eflag_global = vflag_global = -1;
 
+  dt_default = 1;
   unit_style = NULL;
   set_units("lj");
 
@@ -121,6 +126,8 @@ void Update::set_units(const char *style)
   // http://physics.nist.gov/cuu/Constants/Table/allascii.txt
   // using thermochemical calorie = 4.184 J
 
+  double dt_old = dt;
+
   if (strcmp(style,"lj") == 0) {
     force->boltz = 1.0;
     force->hplanck = 1.0;
@@ -295,6 +302,14 @@ void Update::set_units(const char *style)
   int n = strlen(style) + 1;
   unit_style = new char[n];
   strcpy(unit_style,style);
+
+  // check if timestep was changed from default value
+  if (!dt_default && (comm->me == 0)) {
+    error->warning(FLERR,fmt::format("Changing timestep from {:.6} to {:.6} "
+                                     "due to changing units to {}",
+                                     dt_old, dt, unit_style));
+  }
+  dt_default = 1;
 }
 
 /* ---------------------------------------------------------------------- */
diff --git a/src/update.h b/src/update.h
index 558719f4cc..1d1e04b8bd 100644
--- a/src/update.h
+++ b/src/update.h
@@ -37,6 +37,7 @@ class Update : protected Pointers {
   int setupflag;                  // set when setup() is computing forces
   int post_integrate;             // 1 if now at post_integrate() in timestep
   int multireplica;               // 1 if min across replicas, else 0
+  int dt_default;                 // 1 if dt is at default value, else 0
 
   bigint eflag_global,eflag_atom;  // timestep global/peratom eng is tallied on
   bigint vflag_global,vflag_atom;  // ditto for virial