From 6b3e16ad9cc43b9a2c1738317c4fb1b0238d009d Mon Sep 17 00:00:00 2001
From: Giacomo Fiorin <giacomo.fiorin@gmail.com>
Date: Wed, 3 May 2023 10:33:39 -0400
Subject: [PATCH] Use calcenergy & calcforces to avoid evolving the bias during
 exchanges

---
 colvartools/namd/colvars_replica_utils.tcl | 6 ++++--
 doc/cvscript-fix-modify.tex                | 2 +-
 doc/cvscript-tcl.tex                       | 2 +-
 src/colvarscript_commands_bias.h           | 5 +++--
 4 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/colvartools/namd/colvars_replica_utils.tcl b/colvartools/namd/colvars_replica_utils.tcl
index 1dddcb5c9..a2ccc8bf8 100644
--- a/colvartools/namd/colvars_replica_utils.tcl
+++ b/colvartools/namd/colvars_replica_utils.tcl
@@ -174,7 +174,8 @@ proc select_bias { i_bias } {
     # Now turn on the selected one
     foreach bias_name $bias_names(${i_bias}) {
         cv bias ${bias_name} set active 1
-        cv bias ${bias_name} update
+        cv bias ${bias_name} calcenergy
+        cv bias ${bias_name} calcforces
     }
 
     # The dependency system may have turned off some variables, reactivate them
@@ -215,7 +216,8 @@ proc share_bias_state { bias_name this_replica i j } {
     }
     if { ${this_replica} == ${j} } {
         cv bias ${bias_name} loadfromstring [replicaRecv ${i}]
-        cv bias ${bias_name} update
+        cv bias ${bias_name} calcenergy
+        cv bias ${bias_name} calcforces
     }
 }
 
diff --git a/doc/cvscript-fix-modify.tex b/doc/cvscript-fix-modify.tex
index 1a0a4f813..27e35b9d4 100644
--- a/doc/cvscript-fix-modify.tex
+++ b/doc/cvscript-fix-modify.tex
@@ -644,7 +644,7 @@
 \begin{mdexampleinput}{}
 \texttt{\textbf{fix\_modify Colvars bias name calcforces}}
 \\
-\-~~~~\texttt{Recalculate the forces of this bias at the current colvar values}
+\-~~~~\texttt{Recalculate the forces of this bias after a call to calcenergy}
 \\
 \-~~~~\texttt{\textbf{Returns}}
 \\
diff --git a/doc/cvscript-tcl.tex b/doc/cvscript-tcl.tex
index e1e59467c..2eae9472a 100644
--- a/doc/cvscript-tcl.tex
+++ b/doc/cvscript-tcl.tex
@@ -644,7 +644,7 @@
 \begin{mdexampleinput}{}
 \texttt{\textbf{cv bias name calcforces}}
 \\
-\-~~~~\texttt{Recalculate the forces of this bias at the current colvar values}
+\-~~~~\texttt{Recalculate the forces of this bias after a call to calcenergy}
 \\
 \-~~~~\texttt{\textbf{Returns}}
 \\
diff --git a/src/colvarscript_commands_bias.h b/src/colvarscript_commands_bias.h
index 3c211c088..facfa802d 100644
--- a/src/colvarscript_commands_bias.h
+++ b/src/colvarscript_commands_bias.h
@@ -77,7 +77,8 @@ CVSCRIPT(bias_calcenergy,
          "E : float - Energy value",
          0, 0,
          "",
-         if (this_bias->calc_energy(NULL) != COLVARS_OK) {
+         if ( ( this_bias->colvarbias::update() |
+                this_bias->calc_energy(NULL) ) != COLVARS_OK) {
            script->add_error_msg("Error: recalculating energy of bias " +
                                  this_bias->name);
            return COLVARSCRIPT_ERROR;
@@ -87,7 +88,7 @@ CVSCRIPT(bias_calcenergy,
          )
 
 CVSCRIPT(bias_calcforces,
-         "Recalculate the forces of this bias at the current colvar values\n"
+         "Recalculate the forces of this bias after a call to calcenergy\n"
          "forces : array of colvarvalue objects - Applied colvar forces",
          0, 0,
          "",