@Frederick_Lost, an excellent suggestion, and to think it just takes 4 lines of code !
I tried out, it worked fine, though without checking out the graph. Then I saw @rsdimitrov’s comment, checked out the graph and it was fine. Huh?
Compared his code with yours (the one I had copied): they’re identical. Huh?
Ah, I see, you corrected your original 
So, thank you both for this !! 