From 78d27e991873afd8d40605fc2e41b4885d96c8dc Mon Sep 17 00:00:00 2001
From: Daniele <Iximiel@users.noreply.github.com>
Date: Wed, 9 Oct 2024 14:52:06 +0200
Subject: [PATCH] FIX-2.9 Now the forces from LWALLS should be correct  (#1111)

* Now the forces from LWALLS should be correct (and maybe also the energies)

* now the documentation reflects the code better
---
 src/bias/LWalls.cpp | 8 +++++++-
 src/bias/UWalls.cpp | 6 ++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/bias/LWalls.cpp b/src/bias/LWalls.cpp
index 5e6834234a..dc39572687 100644
--- a/src/bias/LWalls.cpp
+++ b/src/bias/LWalls.cpp
@@ -35,10 +35,16 @@ The restraining potential starts acting on the system when the value of the CV i
 minus an offset \f$o_i\f$ (OFFSET).
 The expression for the bias due to the wall is given by:
 
+for UPPER_WALLS:
 \f$
   \sum_i {k_i}((x_i-a_i+o_i)/s_i)^e_i
 \f$
 
+for LOWER_WALLS:
+\f$
+  \sum_i {k_i}|(x_i-a_i-o_i)/s_i|^e_i
+\f$
+
 \f$k_i\f$ (KAPPA) is an energy constant in internal unit of the code, \f$s_i\f$ (EPS) a rescaling factor and
 \f$e_i\f$ (EXP) the exponent determining the power law. By default: EXP = 2, EPS = 1.0, OFFSET = 0.
 
@@ -133,7 +139,7 @@ void LWalls::calculate() {
     if( lscale < 0.) {
       const double k=kappa[i];
       const double exponent=exp[i];
-      double power = std::pow( lscale, exponent );
+      double power = std::pow( -lscale, exponent );
       f = -( k / epsilon ) * exponent * power / lscale;
       ene += k * power;
       totf2 += f * f;
diff --git a/src/bias/UWalls.cpp b/src/bias/UWalls.cpp
index 0abc063f9e..357b1c3b5a 100644
--- a/src/bias/UWalls.cpp
+++ b/src/bias/UWalls.cpp
@@ -35,10 +35,16 @@ The restraining potential starts acting on the system when the value of the CV i
 minus an offset \f$o_i\f$ (OFFSET).
 The expression for the bias due to the wall is given by:
 
+for UPPER_WALLS:
 \f$
   \sum_i {k_i}((x_i-a_i+o_i)/s_i)^e_i
 \f$
 
+for LOWER_WALLS:
+\f$
+  \sum_i {k_i}|(x_i-a_i-o_i)/s_i|^e_i
+\f$
+
 \f$k_i\f$ (KAPPA) is an energy constant in internal unit of the code, \f$s_i\f$ (EPS) a rescaling factor and
 \f$e_i\f$ (EXP) the exponent determining the power law. By default: EXP = 2, EPS = 1.0, OFFSET = 0.