Greek numbering

Question

I wish to use numbering like 1\alpha, 1\beta,... in some subequations. I know that this is obtainable by redefining the \theequation like the following (which gives lower-case Roman numerals, 1.i, 1.ii,...)

\begin{subequations}
\renewcommand{\theequation}{\theparentequation{}.\roman{equation}}
\begin{align}
  a1 &= b1 \\
  a2 &= b2
\end{align}
\end{subequations}

The problem is I don't know the equivalent of \roman that will yield the Greek alphabet.

A related question (which might subsume the above) is: can someone complete the set of commands

\arabic, \alph, \Alph, \roman, \Roman, ...

Answer 1

You can create a Greek equivalent by taking the code of e.g. \alph from the file latex.ltx and modify it to get what you want. It also requires a slight modification to the subequations environment from amsmath.

\documentclass[11pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}

\makeatletter
\newcommand*{\greek}[1]{%
  \expandafter\@greek\csname c@#1\endcsname
}
\newcommand*{\@greek}[1]{%
  $\ifcase#1\or\alpha\or\beta\or\gamma\or\delta\or\varepsilon
    \or\zeta\or\eta\or\theta\or\iota\or\kappa\or\lambda
    \or\mu\or\nu\or\xi\or o\or\pi\or\varrho\or\sigma
    \or\tau\or\upsilon\or\phi\or\chi\or\psi\or\omega
    \else\@ctrerr\fi$
}
\renewenvironment{subequations}{%
  \refstepcounter{equation}%
  \protected@edef\theparentequation{\theequation}%
  \setcounter{parentequation}{\value{equation}}%
  \setcounter{equation}{0}%
  \def\theequation{\theparentequation\greek{equation}}%
  \ignorespaces
}{%
  \setcounter{equation}{\value{parentequation}}%
  \ignorespacesafterend
}
\makeatother

\begin{document}
  \begin{subequations}
    \begin{align}
      (a+b)^2 &= a^2+2ab+b^2 \\
      (a-b)^2 &= a^2-2ab+b^2 \\
      (a+b)(a-b) &= a^2-b^2
    \end{align}
  \end{subequations}
\end{document}

You mentioned that you only want to modify some equations. The above introduced approach is a general modification. So you might have to do some adjustment on your own. At least you have Greek letters as enumeration symbols which also could be used at other places.

Answer 2

Taking inspiration from T.D.'s excellent answer, I wrote a small package to add extra counter output types. As well as greek, it defines binary, hexadecimal, and "First, Second, Third...".

• morenum.sty on github
• moreenum on CTAN

Answer 3

You can use the \greeknumeral or \Greeknumeral from the babel package. I am not sure how well they will play within a maths environment, but you can read the source for some inspiration.

Answer 4

There is no LaTeX2e equivalent for Greek letters. The only numbering command you're missing there is \fnsymbol, which is actually how you'll implement support for Greek letters yourself. \fnsymbol is (from source2e.pdf)

\def\fnsymbol#1{\expandafter\@fnsymbol\csname c@#1\endcsname}

and \@fnsymbol is

\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}}

So to define your own numbering scheme, just define a new macro along similar lines and insert the appropriate symbols.

There may be a package that does this already; another package along similar lines is alphalph which lets you display alphabetically numbers greater than 26: {A, …, X, Y, Z, AA, AB, …, ZZ, AAA, AAB, …, FXSHRXW}