CS2Backbone: fix a bug when using more than 2 chains

CHANGES/v2.4.md

@@ -207,6 +207,7 @@ For users:
   - Fix some performances regression issue with OpenMP
   - Updated NAMD patches to version 2.12 and 2.13. Old patches have been removed.
   - GROMACS patch for gromacs-2018.4.
+  - Fix a bug in CS2BACKBONE when using more than 2 chains
 
 For developers:
   - Small fix in LDFLAGS when enabling coverage.

src/isdb/CS2Backbone.cpp

@@ -1476,7 +1476,7 @@ void CS2Backbone::init_sidechain(const PDB &pdb) {
       }
 
     }
-    old_size += aend.index()+1;
+    old_size = aend.index()+1;
   }
 }
 
@@ -1566,7 +1566,7 @@ void CS2Backbone::init_xdist(const PDB &pdb) {
         atom[s][a].xd2.push_back(add2);
       }
     }
-    old_size += aend.index()+1;
+    old_size = aend.index()+1;
   }
 }
 
@@ -1689,7 +1689,7 @@ void CS2Backbone::init_rings(const PDB &pdb) {
         plumed_merror("Unkwown Ring Fragment");
       }
     }
-    old_size += aend.index()+1;
+    old_size = aend.index()+1;
   }
 }