two values of the matrix A are changing as you can see in the picture. Why is this happening? What can I do to solve it?
I tried 'Execute the entire worksheet' but could not solve it.
The Matrix which you first assign to A contains the name C in the formulas used for both the A[2,3] and A[3,2] entries.
And then you assign a Vector to the name C.
So, of course, that affects those two entries of A.
If you don't want that to happen then choose use two different names for the two different purposes, eg. C for the Vector and CP in the entries, or vice versa.
You will always run into trouble if you try to use the same name to mean two different things. That's not just a Maple issue: it'll happen to you in math, and in other programming languages.