no n^2 for _fc

python/scontact.py

@@ -168,6 +168,8 @@ class ParticleProblem :
             return np.array([],np.int32)
     
     def previousContactForces(self):
+        if self._fc is None:
+            self._fc = np.zeros_like(self.velocity())
         return(self._fc)
 
     def set_boundary_velocity(self, tag, v) :
@@ -352,7 +354,6 @@ class ParticleProblem :
         tag -- particle tag
         """
         self._lib.particleProblemAddParticle(self._p, self._coord_type(*x), c_double(r), c_double(m), tag.encode())
-        self._fc = np.zeros_like(self.velocity())
 
     def set_use_queue(self, use_queue=1):
       """Enables the use of the queue if 1 and disables it if 0."""