+ scalar_t speed = sqrt(_dcenter_x * _dcenter_x + _dcenter_y * _dcenter_y);
+ scalar_t speed_target = speed_max - exp(-speed / speed_max) * speed_max;
+
+ _dcenter_x = speed_target * _dcenter_x / speed;
+ _dcenter_y = speed_target * _dcenter_y / speed;
+