From 92cc30e7ba42fd26bc0795626fa5dbf401ed0e0d Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Fri, 23 Apr 2021 05:13:36 -0400
Subject: [PATCH] correctly determine the number of active pair style instances

---
 src/SPIN/compute_spin.cpp | 17 ++++++++++-------
 src/SPIN/fix_nve_spin.cpp | 17 ++++++++++-------
 src/pair_hybrid.h         |  4 +++-
 3 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/src/SPIN/compute_spin.cpp b/src/SPIN/compute_spin.cpp
index 9108cd7dfa..26b02aa7c3 100644
--- a/src/SPIN/compute_spin.cpp
+++ b/src/SPIN/compute_spin.cpp
@@ -82,15 +82,18 @@ void ComputeSpin::init()
 
   // loop 1: obtain # of Pairs, and # of Pair/Spin styles
 
-  if (force->pair_match("spin",0,0)) {        // only one Pair/Spin style
-    pair = force->pair_match("spin",0,0);
-    npairs = pair->instance_total;
+  PairHybrid *hybrid = (PairHybrid *)force->pair_match("^hybrid",0);
+  if (force->pair_match("^spin",0,0)) {        // only one Pair/Spin style
+    pair = force->pair_match("^spin",0,0);
+    if (hybrid == nullptr) npairs = 1;
+    else npairs = hybrid->nstyles;
     npairspin = 1;
-  } else if (force->pair_match("spin",0,1)) { // more than one Pair/Spin style
-    pair = force->pair_match("spin",0,1);
-    npairs = pair->instance_total;
+  } else if (force->pair_match("^spin",0,1)) { // more than one Pair/Spin style
+    pair = force->pair_match("^spin",0,1);
+    if (hybrid == nullptr) npairs = 1;
+    else npairs = hybrid->nstyles;
     for (int i = 0; i<npairs; i++) {
-      if (force->pair_match("spin",0,i)) {
+      if (force->pair_match("^spin",0,i)) {
         npairspin ++;
       }
     }
diff --git a/src/SPIN/fix_nve_spin.cpp b/src/SPIN/fix_nve_spin.cpp
index 855b82c30e..0c6a19b4ca 100644
--- a/src/SPIN/fix_nve_spin.cpp
+++ b/src/SPIN/fix_nve_spin.cpp
@@ -172,15 +172,18 @@ void FixNVESpin::init()
 
   // loop 1: obtain # of Pairs, and # of Pair/Spin styles
 
-  if (force->pair_match("spin",0,0)) {        // only one Pair/Spin style
-    pair = force->pair_match("spin",0,0);
-    npairs = pair->instance_total;
+  PairHybrid *hybrid = (PairHybrid *)force->pair_match("^hybrid",0);
+  if (force->pair_match("^spin",0,0)) {        // only one Pair/Spin style
+    pair = force->pair_match("^spin",0,0);
+    if (hybrid == nullptr) npairs = 1;
+    else npairs = hybrid->nstyles;
     npairspin = 1;
-  } else if (force->pair_match("spin",0,1)) { // more than one Pair/Spin style
-    pair = force->pair_match("spin",0,1);
-    npairs = pair->instance_total;
+  } else if (force->pair_match("^spin",0,1)) { // more than one Pair/Spin style
+    pair = force->pair_match("^spin",0,1);
+    if (hybrid == nullptr) npairs = 1;
+    else npairs = hybrid->nstyles;
     for (int i = 0; i<npairs; i++) {
-      if (force->pair_match("spin",0,i)) {
+      if (force->pair_match("^spin",0,i)) {
         npairspin ++;
       }
     }
diff --git a/src/pair_hybrid.h b/src/pair_hybrid.h
index ca79163fc2..1279bc04fa 100644
--- a/src/pair_hybrid.h
+++ b/src/pair_hybrid.h
@@ -25,13 +25,15 @@ PairStyle(hybrid,PairHybrid)
 namespace LAMMPS_NS {
 
 class PairHybrid : public Pair {
+  friend class ComputeSpin;
   friend class FixGPU;
   friend class FixIntel;
   friend class FixOMP;
+  friend class FixNVESpin;
   friend class Force;
+  friend class Info;
   friend class Neighbor;
   friend class Respa;
-  friend class Info;
   friend class PairDeprecated;
  public:
   PairHybrid(class LAMMPS *);