TST: change an objective function in a differential evolution regress…

…ion test

scipy/optimize/tests/test__differential_evolution.py

@@ -362,14 +362,8 @@ def test_gh_4511_regression(self):
         # uses a custom popsize that had triggered an off-by-one error.
         # Because we do not care about solving the optimization problem in
         # this test, we use maxiter=1 to reduce the testing time.
-
-        def ackley(x):
-            arg1 = -0.2 * np.sqrt(0.5 * (x[0] ** 2 + x[1] ** 2))
-            arg2 = 0.5 * (np.cos(2. * np.pi * x[0]) + np.cos(2. * np.pi * x[1]))
-            return -20. * np.exp(arg1) - np.exp(arg2) + 20. + np.e
-
         bounds = [(-5, 5), (-5, 5)]
-        result = differential_evolution(ackley, bounds, popsize=1815, maxiter=1)
+        result = differential_evolution(rosen, bounds, popsize=1815, maxiter=1)
 
 
 if __name__ == '__main__':