def create_new_dir(self, prefix="./", root="Sims"):
        """
Create the directory where to put the simulation
"""
        self.dirRoot = os.path.join(prefix, root)

        today = datetime.date.today()
        free = False
        index = 0

        dirDate = today.strftime("%d-%m-%Y")

        dirComp = os.path.join(self.dirRoot, dirDate)
        dir = os.path.join(dirComp, "Sim_" + str(index))
        while not free :
            if os.path.exists(dir):
                index = index + 1
                simNum = "Sim_" + str(index)
                dir = os.path.join(dirComp, simNum )
            else:
                free = True
                os.makedirs(dir)
        return dir