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?
\mathit{\mathbf{X}}
but that's more of a LaTex stackexchange question already asked. $\endgroup$ – user645636 May 7 '19 at 15:41