add functionality to have a record of cost_opti

Appli-iso3dfd/ACO.py

@@ -84,6 +84,8 @@ def ACO(Me, NbP, comm, alpha, rho, Q, nb_ants, tau_0, n_iter, n1_max=256, n2_max
             if best_cost < cost_opti:
                 cost_opti = best_cost
                 path_opti = best_p
+            with open("cost_opti.txt", 'a') as file:
+                file.write(f"{-1*cost_opti}\n")
         comm.Bcast(tau, root=0)
 
     if Me == 0: