how to make a vector z that consists of odd-indexed entries of y (y=[100:1])?

y=[100:1];

>> z=

Answer 1

[KSSV]

y = 1:2:100

Answer 2

[John D'Errico]

A very confusing question. I'll take a wild guess. If this does not answer your question, then you need to be FAR more lear.

y = primes(20)

y = 1×8

2 3 5 7 11 13 17 19

Now take the elements of y with odd indexes. That is, start at index 1, then 3, then 5, then 7, etc.

z = y(1:2:end)

z = 1×4

2 5 11 17

But maybe you want to know the indexes of the elements in the arry that are odd numbers. How can I possibly know from your question?

u = find(mod(y,2) == 1)

u = 1×7

2 3 4 5 6 7 8

As you can see, all primes in that list except for the first are odd numbers.