# Math expression and number in text mode

I am writing an article for an IEEE journal. At one paragraph, I put explanation about a preceding equation like this:

where c1 = 0.0123 is a coefficient from this document.

My question, how should I type it in my latex document? Should I type the math expression this way: `\$c_{1} = 0.0123\$`, or can I do it this way: `\$c_{1}\$ = 0.0123`, or maybe like this: `\$c_{1} =\$ 0.0123`? Please attach some dependable sources if possible.

• The first, otherwise the spacing around the = will be wrong and, in general, the digits in the left will be in a different font to those on the right (this is a duplicate I think, I will see if I can find...) – David Carlisle Mar 9 '17 at 12:08
• I would argue if the journal has no specific rules, do it the way you want, and try to be consistent throughout the whole document. Further, remember that your document will be typesetted by (hopefully) professional editors, who should be able to modify things if they do not match the journals design. @David: One could also argue to use the third, since this provides consistency of number fonts in the complete document, otherwise you would have to put all numeric values in math mode. – Timm Mar 9 '17 at 12:09
• See for example Knuth's comments linked from tex.stackexchange.com/a/37191/1090 – David Carlisle Mar 9 '17 at 12:11
• @Timm the second with `=\$` is definitely wrong. The third if it is text not math should be `c\textsubscript{1} = 0.0123` otherwise you are relying on the (not generally true) assumption that the digits in math and the digits in text are using the same font. using different fonts for digits in the same equation would be weird. – David Carlisle Mar 9 '17 at 12:15

If

c1 = 0.0123

is text then it should be marked up as

``````c\textsubscript{1} = 0.0123
``````

If it is math then it should be marked up as

``````\$ c_1 = 0.0123 \$
``````

Using half text and half math for the same expression will produce poor spacing and/or inconsistent fonts.

Knuth in his paper cited in the answer to a related question describes an issue where he'd marked up positive numbers as `1` and negative numbers as `\$-1\$` and then got caught out when changing the document's font setup so that math digits used a different font from text digits which had the unwanted consequence of making negative and positive numbers use different fonts. The strong recommendation is to always use math mode for math, even if it is just a minimal expression such as `\$1\$` or `\$x\$`.