For loop with matrix

As ttkoro has shown, you have forgotten the vector index at z and you had put the increment of i outside and after the loop. So actually you applied the calculation six times to the first vector element and then you got this single value as your result.

But why not simply

If you insist on using a loop, you could do it a bit shorter like this

Note the that local variable in the program must not have the same name as the variable you intend to assign the result to. But of course there is nothing wrong if you use a local variable "z" instead of  "Result".