Sorry, but there is not a feature like that for matrices in TI-basic. I am aware of a different way to do the same thing though: Are you allowed to use lists instead of matrices? I don't know if you're familiar with how lists on the calc work, but if you store all of your "z" values into L1 and all of your "y" values into L2, you can then do the same thing you wanted with this bit of code:

```
:Input "Z=",Z
:Disp L2(dim(L1)+1-sum(cumSum(L1=Z
```

That worked for me. It's probably horribly unoptimized, as I haven't programmed in Basic in a while, but it gets the job done.

To generalize, if you have a number Z and you want to find what number element of the list L1 it is, then do dim(L1)+1-sum(cumSum(L1=Z)) to find what number element it is. Again, apologies if there is a simpler way to do it, but the easiest way I could find used all those fancy tokens.

Hope that helps,

42maelstrom