What is the advantage of using $f^\prime$ instead of $f'$?

Question

Although the two outputs look quite similar, what is the advantage of using $f^\prime$ instead of $f'$ ? By the way, here is my code:

\documentclass‎{article‎}‎
\begin{document}‎‎‎
\[‎ ‎f^‎\prime ‎(x)=y‎ ‎\]‎
\[‎ ‎f'‎ ‎(x)=y‎ ‎\]‎‎
\end{document}

There's no advantage in using $f^\prime$ ; it's just more awkward to type than $f'$ and the result is exactly the same. — egreg, Dec 15 '12 at 17:14
Actually, there is one situation you need ^\prime; when you want to make a parenthesis around the \prime so that you denote it applies to un-primed and primed respectively, you cannot do something like $f^('^)$ , you would need $f^{(\prime)}$ . — Hojin Cho, Sep 13 '22 at 12:03

score 155 · Accepted Answer · edited Dec 01 '16 at 14:31

TL;DR: ' is a shorthand for ^{\prime}.

' is defined in latex.ltx as active math character:

\def\active@math@prime{^\bgroup\prim@s}
{\catcode`\'=\active \global\let'\active@math@prime}
\def\prim@s{%
  \prime\futurelet\@let@token\pr@m@s}
\def\pr@m@s{%
  \ifx'\@let@token
    \expandafter\pr@@@s
  \else
    \ifx^\@let@token
      \expandafter\expandafter\expandafter\pr@@@t
    \else
      \egroup
    \fi
  \fi}
\def\pr@@@s#1{\prim@s}
\def\pr@@@t#1#2{#2\egroup}

The active ' looks for following ' and puts them together as superscript, a''' becomes a^{\prime\prime\prime}. Thus using ' makes the input easier to write.

score 17 · Answer 2 · answered Jan 26 '15 at 09:32

17

Sometimes you may want to pass LaTeX code as an argument to another program. In that case the code is typically wrapped in quotes. Using quote to mean a prime will confuse the second program. For example to type TeX in graphical output of MATLAB one may use something like

str='$$F^\prime$$'
text(0,0,str,'Interpreter','latex')

to print $F'$ at location $(0,0)$. Using $F'$ in the code however becomes problematic.

answered Jan 26 '15 at 09:32

Maesumi

9,059

1

use double quotes or escapes for the String? – MaxNoe Jan 26 '15 at 10:21
2

@MaxNoe Double quotes don't work in Matlab. String escaping is done with a double quote. So you'd have to write things like 'The symbol f'' is used to represent the first derivative of a function', which looks wrong at a first glance. All things considered, f^\prime doesn't look so bad. – Federico Poloni Feb 09 '15 at 22:18

score 8 · Answer 3 · answered May 16 '17 at 15:00

8

Tl;DR: You can use \prime with additional superscripts.

There is certainly one advantage to using \prime under a particular situation. Suppose you have a map \pi which necessitates the use of another map \pi', which at first seems to be appropriately named.

That is, until you have to pullback something with respect to \pi'. Now you can either write (\pi')^* or \pi^{\prime,*}. The latter looks, arguably, a little better.

But both look horrible.

answered May 16 '17 at 15:00

Emre

193

9

\pi'^{,*} is perfectly equivalent to \pi^{\prime,*} – egreg May 16 '17 at 15:11
2

@egreg \pi'^{,*} fails with error "double superscript"; \pi^{\prime,*} doesn't (using scrartcl and amsmath). So I prefer the latter … ;-) – CL. Feb 06 '19 at 11:32
@CL. Works for me with a minimal document. Some more details would be necessary. – egreg Feb 06 '19 at 12:08
@egreg Figured it out. It's the breqn package that breaks it. MWE. – CL. Feb 06 '19 at 13:10
4

@CL. Besides equations, breqn breaks so many things… – egreg Feb 06 '19 at 13:27
@MWE And now, OverLeaf decided that using ' would be against its syntax commands. Possibly for that very reason. – Alex Sep 07 '19 at 20:50

score 2 · Answer 4 · answered Jan 10 '19 at 12:02

2

I give a practical difference for Emacs users.

If you write $x^{\prime\prime}$ it is all right, if you write $x''$ you completely mess up the AUCTeX syntax coloring.

answered Jan 10 '19 at 12:02

Nisba

651

1

Which version opf AUCTEX, I have no issues with $x''$ – daleif Jan 10 '19 at 12:21
"12.1.1" I am using the default latex configuration of the latest release version of Spacemacs, so I guess many other people share my latex setting – Nisba Jan 10 '19 at 12:25
1

Interesting, I still use 11.90. Just had a PhD student come by yesterday, who also had problems with AUCTEX 12.1.1, which went away when he downgraded (he installed the Emacs + auctex for Windows there is on CTAN, instead). Seems like I'd better stay of 12.1 for while. Perhaps you should mention this on the auctex mailiing this such that they are aware of the issue. – daleif Jan 10 '19 at 13:44
1

I reported the issue – Nisba Jan 10 '19 at 14:11

score 1 · Answer 5 · answered Jul 19 '16 at 07:25

1

In fact, there's a slight difference when you have two superscripts. For instance:

{\bar{e}_k}^{\prime\dag}
{\bar{e}_k}^{'\dag}

The first one fits better.

answered Jul 19 '16 at 07:25

R.Trentini

11

1

Sure, but that's related to ' being the same as ^{\prime}, so if you have foo^{'\dag} your prime symbol is superscripted twice. {\bar{e}_k}'^{\dag} will give identical output as far as my eye can tell, but I agree your input is more elegant. Also fiddling with the my input led me to a double superscript error, which is frankly what I expected to begin with, so using foo^{\prime\dag} is definitely a nice idea here, I think – Au101 Jul 19 '16 at 07:32
8

You should type \bar{e}_k'^{\dag} (the braces around \bar{e}_k do nothing). – egreg Jul 19 '16 at 13:54

score 1 · Answer 6 · answered Nov 06 '18 at 15:28

Although ' is a shorthand for ^\prime as noted in answers above, this can get in your way when dealing with multiple superscripts in combination with subscripts:

\pi_{s+r}^{\ast\prime} = 
\pi^{\ast\prime}_{s+r} \ne 
\pi^{\ast}'_{s+r}      \ne 
\pi_{s+r}^{\ast}'

What is the advantage of using $f^\prime$ instead of $f'$?

6 Answers6

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