Initialize unused velocity constraint components

With domain decomposition, velocity components for communicated
atoms could be uninitialized. These components were never used, but
this could lead to valgrind warnings and floating point exceptions.

Fixes #1576.

Change-Id: Ic673680699578ddf62c2d240342138cbc16490c8

diff --git a/src/gromacs/mdlib/constr.c b/src/gromacs/mdlib/constr.c
index fa8275083dd126e2334755dcbc796210799e48de..b6878e6bd12107d9bb4faf3e298b2f8c4853a758 100644 (file)
--- a/src/gromacs/mdlib/constr.c
+++ b/src/gromacs/mdlib/constr.c
@@ -203,6 +203,18 @@ int n_flexible_constraints(struct gmx_constr *constr)
     return nflexcon;
 }
 
+static void clear_constraint_quantity_nonlocal(gmx_domdec_t *dd, rvec *q)
+{
+    int nonlocal_at_start, nonlocal_at_end, at;
+
+    dd_get_constraint_range(dd, &nonlocal_at_start, &nonlocal_at_end);
+
+    for (at = nonlocal_at_start; at < nonlocal_at_end; at++)
+    {
+        clear_rvec(q[at]);
+    }
+}
+
 void too_many_constraint_warnings(int eConstrAlg, int warncount)
 {
     const char *abort = "- aborting to avoid logfile runaway.\n"
@@ -431,6 +443,15 @@ gmx_bool constrain(FILE *fplog, gmx_bool bLog, gmx_bool bEner,
     if (cr->dd)
     {
         dd_move_x_constraints(cr->dd, box, x, xprime, econq == econqCoord);
+
+        if (v != NULL)
+        {
+            /* We need to initialize the non-local components of v.
+             * We never actually use these values, but we do increment them,
+             * so we should avoid uninitialized variables and overflows.
+             */
+            clear_constraint_quantity_nonlocal(cr->dd, v);
+        }
     }
 
     if (constr->lincsd != NULL)