'Do an optimization run for differential_evolution'

def run_differentialevolution(self):

    self.function.nfev = 0
    t0 = time.time()
    res = differential_evolution(self.fun, self.bounds, popsize=20)
    t1 = time.time()
    res.success = self.function.success(res.x)
    res.nfev = self.function.nfev
    self.add_result(res, (t1 - t0), 'DE')
