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This question is also related to English, but I decided to post thread here as it may have different usage in mathematics.

In numbers, when we say the order, we say, 1st, 2nd, 3rd etc. Those "st" and "nd" changes depending on the number.

The question is what is the correct usage when I want to express the line and column in matrix. For example, i-th row and j-th column? Is is correct to use "th" in case?

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Yes: it is correct to talk about the ith column or the jth row. It would be strange and incorrect to talk about the ind column or the jst row (I don't even know how you would pronounce those).

The same usage applies to any letter of the English alphabet - you can would talk about the pth prime number or the kth entry of the nth row of Pascal's triangle.

In all of these cases, you pronounce them by saying the name of the letter followed by "th", so that ith is /aɪθ/, jth is /dʒeɪθ/, pth is /piːθ/, etc.

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  • $\begingroup$ Thanks @senshin ! I believe this will be very helpful to those whose native language is not English. :) $\endgroup$ – Askar May 5 '14 at 8:31
  • $\begingroup$ @bof I've heard both "i plus oneth" and "i plus first". I think both are acceptable. I would refer to the row indexed by $i^3$ as the "i cubed row" with no ordinal marker, simply because "i cubedth row" is a mouthful. $\endgroup$ – senshin May 5 '14 at 8:32

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