You have defined z as a range, that is something completely different from a vector. And it is important that you understand that.
A Vector is a (single) column Matrix. Both a Vector and a Matrix are forms of an Array. Array's are mathematical constructs that you can Index, that is, you can point at an individual element of the Array.
A Range is just a list of numbers. In Mathcad you can/should use Ranges only to:
- Plot a function (over a range), the range can contain any linear sequence (equally spaced) of real numbers.
- Control a FOR loop in a program, or iterate a (set of) equations on worksheet level, again, the range can contain any real number sequence.
- Index into an Array, in this case the range must consist of integers only.
If you want that matrix, here's what you can do:

In the above program, k is a range used for the second AND the third purpose.
Success!
Luc