Fix output of ATOM section.

Signed-off-by: Timothy Click <tclick@alumni.ou.edu>

src/fluctmatch/topology/RTF.py

@@ -116,7 +116,7 @@ def _write_residues(self, residue):
         key = "ATOM"
         atoms = residue.atoms
         lines = ((atoms.names, atoms.types, atoms.charges)
-                 if not np.issubdtype(atoms.types.dtype, np.signedinteger) else
+                 if np.issubdtype(atoms.types.dtype, np.signedinteger) else
                  (atoms.names, atoms.names, atoms.charges))
         lines = pd.concat([pd.Series(_) for _ in lines], axis=1)
         np.savetxt(self.rtffile, lines, fmt=native_str(self.fmt[key]))