diff --git a/lib/integrator.py b/lib/integrator.py
index a20a639..eebfd00 100755
--- a/lib/integrator.py
+++ b/lib/integrator.py
@@ -24,7 +24,7 @@ def dp_dt(m_array, q_array):
     dp_array[np.isnan(dp_array)] = 0.
     return dp_array
 
-def frogleap(duration, step, dyn_syst, display=False):
+def frogleap(duration, step, dyn_syst, recover_param=False, display=False):
     """
     Leapfrog integrator for first order partial differential equations.
     iteration : half-step drift -> full-step kick -> half-step drift
@@ -34,6 +34,7 @@ def frogleap(duration, step, dyn_syst, display=False):
     q_array = dyn_syst.get_positions()
     p_array = dyn_syst.get_momenta()
     
+    
     if display:
         d = DynamicUpdate()
         d.min_x, d.max_x = -1.5*np.abs(q_array).max(), +1.5*np.abs(q_array).max()
@@ -57,6 +58,7 @@ def frogleap(duration, step, dyn_syst, display=False):
         for i, body in enumerate(dyn_syst.bodylist):
             body.q = q_array[i]
             body.p = p_array[i]
-            body.v = body.p/body.m
-
-    return dyn_syst
+            if body.m != 0.:
+                body.v = body.p/body.m
+    if recover_param:
+        return dyn_syst
diff --git a/main.py b/main.py
index e5e2df3..7f141e3 100755
--- a/main.py
+++ b/main.py
@@ -24,7 +24,8 @@ def main():
         bodylist.append(Body(m[i], q[i], v[i]))
     dyn_syst = System(bodylist)
 
-    new_dyn_syst = frogleap(10, 0.01, dyn_syst, display=True)
+    new_dyn_syst = frogleap(10, 0.1, dyn_syst, display=False)
+    print(np.all(new_dyn_syst.get_positions() == dyn_syst.get_positions()))
     return 0
 
 if __name__ == '__main__':