Alternatives to asterisk and star for superscripts

Question

While writing a paper, I find myself exhausted with superscript symbols to denote similar types of variables. I have used x, x^\ast (i.e. x*), x^\star and x'. I can't use symbols which sit right on top of 'x' such as \hat or \tilde or \bar etc. Neither can I use a new variable (like y or z) for a new quantity related to x. I must also not use a number or an alphabet for the superscript.

I saw some people using alternatives such as big asterisk/star, a club or diamond in the superscript. But these symbols stand out in the text to the extent that they give the text a garish look.

Although I did notice a number of other star/asterisk-related symbols in the comprehensive latex symbol guide, I was not sure which of them is a conventional math superscript.

Any suggestions about using a few more (= 2 or 3) decent superscript symbols? Are there any other commonly used math symbols to solve this problem? Any help will be greatly appreciated. Thanks.

Correction: I am using matrix pseudoinverse in the paper. So, \dagger symbol has also been used.

Answer 1

These symbols remind of footnote symbols, which following this sequence: (1) *, (2), \dagger, (3) \ddagger, (4), \mathsection, (5) \mathparagraph, (6) \|, (7) **, (8) \dagger\dagger and (9) \ddagger\ddagger. You'll notice this sequence when viewing the definition of \@fnsymbol (from latex.ltx):

\def\@fnsymbol#1{\ensuremath{\ifcase#1\or *\or \dagger\or \ddagger\or
   \mathsection\or \mathparagraph\or \|\or **\or \dagger\dagger
   \or \ddagger\ddagger \else\@ctrerr\fi}}

It only carries symbols up to 9, after which an error is thrown. If needed, you can define your own symbol-extraction macro (or use the above) and pick symbols from it in a very generic way:

\documentclass{article}
\makeatletter
\newcommand{\ssymbol}[1]{^{\@fnsymbol{#1}}}
\makeatother
\begin{document}
$x\ x\ssymbol{1}\ x\ssymbol{2}\ x\ssymbol{3}\ x\ssymbol{4}\ x\ssymbol{5}      x\ssymbol{6}\ x\ssymbol{7}\ x\ssymbol{8}\ x\ssymbol{9}$
\end{document}

Perhaps, define your own \@ssymbol macro in a similar way to \@fnsymbol that adds to your symbol selection from those included in the Comprehensive LaTeX symbol list. This is preferred since it also promotes consistency and allows you to easily change your mind later. For example, if you don't want \ddagger\ddagger for \ssymbol{9}, just update the definition and everything else will fall in place; no need to manually replace all \ddagger\ddagger with <new preferres symbol>.

---

As a showcase, \ssymbol{<num>} provides some letters from the Greek alphabet as "symbols":

\documentclass{article}
\usepackage{multido}% http://ctan.org/pkg/multido
\makeatletter
\newcommand{\@ssymbol}[1]{\ifcase#1\or\alpha\or\beta\or\gamma\or\delta\or\epsilon\or\varepsilon
  \or\zeta\or\eta\or\theta\or\vartheta\or\iota\or\kappa\or\lambda\or\mu\or\nu\or\xi\or\pi
  \or\varpi\or\rho\or\varrho\or\sigma\or\varsigma\or\tau\or\upsilon\or\phi\or\varphi\or\chi
  \or\psi\or\omega\else\@ctrerr\fi}
\newcommand{\ssymbol}[1]{^{\@ssymbol{#1}}}
\makeatother
\begin{document}
$x \multido{\i=1+1}{15}{\ x\ssymbol{\i}}$ \par
$x \multido{\i=16+1}{14}{\ x\ssymbol{\i}}$
\end{document}

Answer 2

If there is no prevailing convention, just go ahead and use whatever you want. After all, you only need to introduce it stringently so it's clear from your notation what you want to show. From a readability point of view, it's best to use symbols not easily confused with others. Have a look at the list of LaTeX symbols. Me personally, I'd have a look in Tab. 52. Something like

\Ydown
\Yup
\Yleft
\Yright

Tab. 55 sports some even better symbols, possibly:

\bigvarstar
\divideontimes
\Asterisk
\coAsterisk

Go crazy!

Answer 3

\dagger

There are others available in the same family.

Answer 4

I have found that Latex has a symbol for a star which is the command \bigstar. http://latex.wikia.com/wiki/List_of_LaTeX_symbols

So using the following:

\mathbf{A}_k^{\bigstar}