From 05cafb716fcbafd6e4c8417ea8ab65cd04bbfeb8 Mon Sep 17 00:00:00 2001
From: Tim Mattox <timothy.mattox@engilitycorp.com>
Date: Wed, 18 Jan 2017 15:51:50 -0500
Subject: [PATCH 1/2] USER-DPD: cleanup initialization of splitFDT_flag in
 pair_dpd_fdt.cpp

---
 src/USER-DPD/pair_dpd_fdt.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/USER-DPD/pair_dpd_fdt.cpp b/src/USER-DPD/pair_dpd_fdt.cpp
index f2c4c8f099..332804b8db 100644
--- a/src/USER-DPD/pair_dpd_fdt.cpp
+++ b/src/USER-DPD/pair_dpd_fdt.cpp
@@ -43,6 +43,7 @@ using namespace LAMMPS_NS;
 PairDPDfdt::PairDPDfdt(LAMMPS *lmp) : Pair(lmp)
 {
   random = NULL;
+  splitFDT_flag = false;
 }
 
 /* ---------------------------------------------------------------------- */

From f6cd98636b8ba24ff45029956a3ceb4226c21ba2 Mon Sep 17 00:00:00 2001
From: Tim Mattox <timothy.mattox@engilitycorp.com>
Date: Wed, 18 Jan 2017 16:17:11 -0500
Subject: [PATCH 2/2] USER-DPD: Also apply "check if a0 is zero" optimization
 to pair_dpd_fdt This relates to commit 4eb08a5822 that was applied to
 pair_dpd_fdt_energy

---
 src/USER-DPD/pair_dpd_fdt.cpp | 7 ++++++-
 src/USER-DPD/pair_dpd_fdt.h   | 1 +
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/USER-DPD/pair_dpd_fdt.cpp b/src/USER-DPD/pair_dpd_fdt.cpp
index 332804b8db..e7e9febd82 100644
--- a/src/USER-DPD/pair_dpd_fdt.cpp
+++ b/src/USER-DPD/pair_dpd_fdt.cpp
@@ -44,6 +44,7 @@ PairDPDfdt::PairDPDfdt(LAMMPS *lmp) : Pair(lmp)
 {
   random = NULL;
   splitFDT_flag = false;
+  a0_is_zero = false;
 }
 
 /* ---------------------------------------------------------------------- */
@@ -95,7 +96,7 @@ void PairDPDfdt::compute(int eflag, int vflag)
   // loop over neighbors of my atoms
 
   if (splitFDT_flag) {
-    for (ii = 0; ii < inum; ii++) {
+    if (!a0_is_zero) for (ii = 0; ii < inum; ii++) {
       i = ilist[ii];
       xtmp = x[i][0];
       ytmp = x[i][1];
@@ -288,6 +289,8 @@ void PairDPDfdt::coeff(int narg, char **arg)
   double sigma_one = force->numeric(FLERR,arg[3]);
   double cut_one = cut_global;
 
+  a0_is_zero = (a0_one == 0.0); // Typical use with SSA is to set a0 to zero
+
   if (narg == 5) cut_one = force->numeric(FLERR,arg[4]);
 
   int count = 0;
@@ -372,6 +375,7 @@ void PairDPDfdt::read_restart(FILE *fp)
 
   allocate();
 
+  a0_is_zero = true; // start with assumption that a0 is zero
   int i,j;
   int me = comm->me;
   for (i = 1; i <= atom->ntypes; i++)
@@ -387,6 +391,7 @@ void PairDPDfdt::read_restart(FILE *fp)
         MPI_Bcast(&a0[i][j],1,MPI_DOUBLE,0,world);
         MPI_Bcast(&sigma[i][j],1,MPI_DOUBLE,0,world);
         MPI_Bcast(&cut[i][j],1,MPI_DOUBLE,0,world);
+        a0_is_zero = a0_is_zero && (a0[i][j] == 0.0); // verify the zero assumption
       }
     }
 }
diff --git a/src/USER-DPD/pair_dpd_fdt.h b/src/USER-DPD/pair_dpd_fdt.h
index b90a831cb4..5c20f2fc8f 100644
--- a/src/USER-DPD/pair_dpd_fdt.h
+++ b/src/USER-DPD/pair_dpd_fdt.h
@@ -50,6 +50,7 @@ class PairDPDfdt : public Pair {
   double cut_global;
   int seed;
   bool splitFDT_flag;
+  bool a0_is_zero;
 
   void allocate();