From 405cc128e748b0bae802262953df742abf955139 Mon Sep 17 00:00:00 2001
From: Berk Hess <hess@kth.se>
Date: Mon, 24 Nov 2014 15:36:13 +0100
Subject: [PATCH] Fixed twin-range + freeze + constraints

With twin-range cut-offs, atoms which are both frozen and constrained
would experience very large or NaN forces, leading to constraint
warnings and errors.
Fixes #1639.

Change-Id: I1871a87054fec1149c9ed75872451df79a8ac2d2
---
 src/gromacs/mdlib/update.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/gromacs/mdlib/update.c b/src/gromacs/mdlib/update.c
index 93b7f59c1e..c4bdfe3892 100644
--- a/src/gromacs/mdlib/update.c
+++ b/src/gromacs/mdlib/update.c
@@ -1515,6 +1515,10 @@ static void combine_forces(gmx_update_t upd,
                 {
                     xp[i][d] = state->x[i][d] + fac*f_lr[i][d]*md->invmass[i];
                 }
+                else
+                {
+                    xp[i][d] = state->x[i][d];
+                }
             }
         }
         constrain(NULL, FALSE, FALSE, constr, idef, ir, NULL, cr, step, 0, 1.0, md,
-- 
2.22.0