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I started to read a book about regression analysis, and I faced this latex notation:

$e_i$:s, where $e_i$ is a residual.

What is the meaning of "$:s$"?

Kim
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    Maybe if you can either scan or right down the context, that will help. – Gary. May 24 '15 at 03:52
  • To whom who downvoted the question : if you have no idea, just pass it. Do not think the question is silly or insincerity as if you are so perfect regarding mathematical symbols. How someone can post the question before googled many times? – Kim May 24 '15 at 07:30
  • CONTEXT : this question had, firstly, several downvotes, and blocked with the commend by moderator that it is irrelevant question which implies it might be a confusion. I checked their biography and most of them are from USA or studied in that country, so I was quite upset at that time. – Kim May 26 '15 at 07:20
  • Don't get upset with me, I did not downvote you. And I was asking for the context in which the notation appeared, not about your reaction. – Gary. May 26 '15 at 16:04

1 Answers1

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This is how the plural form of "$e_i$" is denoted, usually (I think) in the writing of European mathematicians. Consider the alternatives:

  • $e_i$s — ugly and very likely to confuse
  • $e_i$'s — looks like grocer's apostrophe

  • $e_i$:s — looks odd if you're unfamiliar with it

  • "numbers/vectors $e_i$" is what I would likely use

  • Yes! That's right! It is written by an author from the EU countries. I guess that's why I suffer to search it!! Thank you so much! – Kim May 24 '15 at 07:07