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I’m writing a scientific text and I’m trying to conform to the ISO 80000-2 standard regarding mathematical notation. After going through the standard there are still two situations I’m unsure about:

Situation 1):

What is the proper typesetting format for variables denoted with subscripts? For example, given the following expression:

$x_{new} = x_{old} + 1$

Should the “new” and “old” text be italic/bold, uppercase/lowercase etc.? Are there any rules for this? ISO 80000-2 does not mention variable names including subscripts as far as I can tell.

Situation 2):

If $\mathbf{X}$ is a matrix, denoted in uppercase, italic, bold. And I want to refer to the first column vector of the matrix, should that be: $\mathbf{x}_1$? I.e., lowercase bold italic to indicate that this is a vector, not a matrix. Or should it be denoted as $\mathbf{X}_1$ to indicate that the quantity is taken from something which is a matrix? Or are both notations wrong?

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  • $\begingroup$ $\boldsymbol{X}$ is denoted in uppercase, italic, bold. $\endgroup$ – Michael Hoppe May 7 '19 at 10:11
  • $\begingroup$ Yes, I know, I just didn’t know how to typeset it that way in the question. What latex command did you use just now to write in bold and italic in math mode? $\endgroup$ – Petahanks May 7 '19 at 11:11
  • $\begingroup$ $\mathit{\mathbf{X}}$ perhaps using \mathit{\mathbf{X}} but that's more of a LaTex stackexchange question already asked. $\endgroup$ – user645636 May 7 '19 at 15:41
  • $\begingroup$ It was \boldsymbol{X}. $\endgroup$ – Michael Hoppe May 7 '19 at 17:34
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You are using 

$x_{new}$

which is wrong anyways. Typeset 

$x_{\text{new}}$

to get $x_{\text{new}}$.

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  • $\begingroup$ Ok, thank you. So you are saying then that subscripts should be written in non-italic, non-bold, lowercase letters? Or is the choice of uppercase/uppercase up to personal taste? Also, are you basing this answer on a standard you can refer me to or is this just your opinion? $\endgroup$ – Petahanks May 7 '19 at 11:16
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    $\begingroup$ I don't know the standards, but I know if you don't surround them with the \text{} part you get then treated as variable names by default in effect with LaTeX and MathJaX. $\endgroup$ – user645636 May 7 '19 at 15:33
  • $\begingroup$ en.m.wikibooks.org/wiki/LaTeX $\endgroup$ – user645636 May 7 '19 at 17:47

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