macrosmath-mode
I defined a macro for writing a partial derivative:
\newcommand{\pder}[2]{\frac{\partial#1}{\partial#2}}
this works when inserting two parameters. But I want to modify it so that when inserting only a single parameter, it will leave the numerator blank and fill only the denominator with that parameter. i.e.,
\pder{x}
will produce
\frac{\partial}{\partial x}
How can I achieve that?
Here's a expl3 version with seq variables.
The command \NewListCommand declares the command list macro named like the first argument and uses a global seq variable with some prefix, see \g_cryingshadow_mynewlist_seq etc.
This is filled by the \mynewlist command and the content displayed depending on the content of the other parameters from #3 to #6. The 7th. parameter is used as a delimiter
Some notes: The empty parameter could be an optional one.
\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\NewListCommand}{mmmmmmm}{%
\seq_new:c {g_cryingshadow_#1_seq} % Make a new sequence
\expandafter\NewDocumentCommand\csname #1\endcsname{m}{%
\seq_gclear:c {g_cryingshadow_#1_seq}% Clear the sequence
\seq_gclear:N \l_tmpa_seq % Clear a temporary `\l_tmpa_seq
\seq_set_split:Nnn \l_tmpa_seq {} {##1} % Split the sequence into tokens.
\seq_set_eq:cN {g_cryingshadow_#1_seq} \l_tmpa_seq % copy the temporary sequence to the real one → this would not be necessary if the sequence is not be used outside
\seq_if_empty:cTF {g_cryingshadow_#1_seq} {%
#2% Checked --> is empty
}{%
% Display the various styles
\int_case:nn { \seq_count:c {g_cryingshadow_#1_seq} }
{%
{1} {#3 \seq_use:cnnn {g_cryingshadow_#1_seq} {,} {#7} {#7} #4}
}%
\int_compare:nNnT { \seq_count:c {g_cryingshadow_#1_seq}} > 1 {%
#5 \seq_use:cnnn {g_cryingshadow_#1_seq} {#7} {#7} {#7} #6
}
}
}
}
\ExplSyntaxOff
\NewListCommand{mynewlist}{empty}{[}{]}{(}{)}{,}
\begin{document}
\mynewlist{{A}{B}{C}}
\mynewlist{{A}{B}}
\mynewlist{{a}}
\mynewlist{}
\mynewlist{{A}{B}{C}{D}{E}{F}}
Astronomer's alphabet:
\mynewlist{{Oh}{be}{a}{fine}{girl}{kiss}{me}}
\end{document}
Edit: Here's the working version for usual LaTeX:
\documentclass{article}
\usepackage{etoolbox}
\makeatletter
\def\definelistcommand#1#2#3#4#5#6#7{%
\expandafter\def\csname @firstinlist#1\endcsname##1{%
\@ifnextchar\@stoplist{%
#3##1#4\@endlist%
}{%
#5##1\csname @nextlist#1\endcsname%
}%
}
\expandafter\def\csname @nextlist#1\endcsname##1{%
\@ifnextchar\@stoplist{%
#7##1#6\@endlist%
}{%
#7##1\csname @nextlist#1\endcsname%
}%
}
\expandafter\def\csname @startlist#1\endcsname##1{%
\@ifnextchar\@stoplist{%
#3##1#4\@endlist%
}{%
\csname @firstinlist#1\endcsname##1%
}%
}
\expandafter\def\csname #1\endcsname##1{%
\ifblank{##1}{%
#2%
}{%
\csname @startlist#1\endcsname##1\@stoplist%
}%
}
}
\def\@endlist#1{}
\definelistcommand{mycmd}{empty}{[}{]}{(}{)}{,}
\definelistcommand{othercmd}{empty}{\textbraceleft}{\textbraceright}{(}{)}{+}
\begin{document}
\makeatother
\mycmd{{A}{B}{C}}
\mycmd{A}
\mycmd{{A}{B}}
\mycmd{}
\othercmd{{O}{B}}
\othercmd{{O}}
\end{document}
Just introduce expandable macros to grab the first or the last digit of the string.
\documentclass{article}
\usepackage{fontspec}
%\setmainfont{STIXTwoText-Regular}
%\newfontfamily\fracfigs{STIXTwoText-Medium}[% compensate weight for scaling
% Numbers = {Proportional,Lining},
% Scale = 0.75]
% Actual kerns wrong for this font, but everyone will have it:
\setmainfont{Latin Modern Roman}
\newfontfamily\fracfigs{Latin Modern Roman}[Scale = 0.75]
\def\getfirst#1#2\relax{#1}
\def\getlast#1#2\relax{\if\relax#2\relax#1\else\getlast#2\relax\fi}
\newcommand*\myFii{2}
\newcommand*\myFiv{4}
\newcommand*\myFvi{6}
\newcommand*\myFvii{7}
\newcommand*\myFix{9}
\newcommand*\myfrac[2]{%
\edef\myfractmpn{\getlast#1\relax}% Really want just last char
\edef\myfractmpd{\getfirst#2\relax}% Really want just first char
\raisebox{0.5ex}{{\fracfigs#1}}%
\ifx\myfractmpn\myFii \kern 0.1em%
\else\ifx\myfractmpn\myFvii \kern -0.05em%
\else\ifx\myfractmpn\myFix \kern 0pt%
\else \kern 0.05em%
\fi\fi\fi%
\textfractionsolidus%
\ifx\myfractmpd\myFiv \kern -0.05em%
\else\ifx\myfractmpd\myFvi \kern 0pt%
\else \kern 0.05em%
\fi\fi%
{\fracfigs#2}}
\begin{document}
\myfrac{1}{1}\quad \myfrac{11}{11}\par
\myfrac{2}{2}\quad \myfrac{22}{22}\par
\myfrac{3}{3}\quad \myfrac{33}{33}\par
\myfrac{4}{4}\quad \myfrac{44}{44}\par
\myfrac{5}{5}\quad \myfrac{55}{55}\par
\myfrac{6}{6}\quad \myfrac{66}{66}\par
\myfrac{7}{7}\quad \myfrac{77}{77}\par
\myfrac{8}{8}\quad \myfrac{88}{88}\par
\myfrac{9}{9}\quad \myfrac{99}{99}\par
\end{document}
Best Answer
The best approach is to make the numerator variable optional:
Now
\pder[f]{x}and\pder{x}will work as you wish.A solution that uses the syntaxes
\pder{f}{x}and\pder{x}iswhich however is quite risky, because an open brace after
\pder{x}will be mistaken for the start of the second argument (spaces are ininfluent). All in all, the optional argument path seems better.If you don't plan to often use
\pderinside moving arguments,\DeclareRobustCommandcan be changed into\newcommand, but the command would be fragile and so needing\protectin front of it when in moving arguments.