I scrolled across the image - jie is already defined as a struct (possibly in the code before this particular lines), thus you can not over-write it using indexing.
You can either
1) Over-write jie completely, like this -
jie = [limit(f, inf) limit(f, +inf) limit(f,-inf)]
or
2) Clear jie and then assign the limit values -
clear jie
jie(1) = limit(f, inf)
jie(2) = limit(f, +inf)
jie(3) = limit(f, -inf)
