Fig. 2

The negative of the gradient vector (bold line segment number 1) and the q-gradient vector of f for different values of the parameter q (line segments from 2 to 10 and 2′ to 10′). The parameters (\(q_1,q_2\)) used for each line segment are 2: (0.97, 1.03), 2′: (1.03, 0.97), 3: (0.9, 1.1), 3′: (1.1, 0.9), 4: (0.8, 1.2), 4′: (1.2, 0.8), 5: (0.7, 1.3), 5′: (1.3, 0.7), 6: (0.6, 1.4), 6′: (1.4, 0.6), 7: (0.5, 1.5), 7′: (1.5, 0.5), 8: \((-1.2,-0.8)\), 8′: \((-0.8,-1.2)\), 9: \((-1.4,-0.6)\), 9′: \((-0.6,-1.4)\), 10: \((-10,-3)\) and 10′: \((-3,-10)\)