I think the grad(f) at 16:00 should be 0.5(S+S tranpose)x-a , right? anyway, thank you for the amazing lecture!####[['lecture', 'Course_General_Feedback', 'POS'], ['NULL', 'Instructor', 'POS'], ['grad(f)', 'Mathematical_Related_Concept', 'NEU'], ['0.5(S+S tranpose)x-a', 'Mathematical_Related_Concept', 'NEU']]