ith, i'th or i-th

[Bart Vandewoestyne]

Suppose you want to write about the point with index i in a
mathematical text. Then how do you write this?

The ith point.
The i'th point.
The i-th point.

I have seen all three forms, but it is not clear to me what form
is the exact one and should be used. Or is this something that
depends on the English dialect used?

Is there a strict grammar rule for this?

Thanks,
Bart

[Miss Elaine Eos]

Post by Bart Vandewoestyne
Suppose you want to write about the point with index i in a
mathematical text. Then how do you write this?
The ith point.
The i'th point.
The i-th point.
I have seen all three forms, but it is not clear to me what form
is the exact one and should be used. Or is this something that
depends on the English dialect used?
Is there a strict grammar rule for this?

I believe that i'th is incorrect. We use "nth" for n, although "ith"
looks funny to me. However, I believe that, as long as the context is
clear (that we're talking about the variable "i"), I think that's the
correct term. I'm pretty sure that i'th and i-th are things made-up by
people who just weren't sure what to do.

[Frederick Williams]

Post by Bart Vandewoestyne
Suppose you want to write about the point with index i in a
mathematical text. Then how do you write this?
The ith point.
The i'th point.
The i-th point.

Handwriting or typeset? It matters because properly typeset
mathematical text will have the "i" italicized, so "The ith point." will
be fine in as much as the "i" will stand out from the "th". "i'th" is
wrong, I would think, because "'" it hints at (at least in this sort of
context) missing letters; none are missing, are they?

"i-th" is fine in handwritten text.