我经常发现自己输入的产品中每个术语看起来都很相似，但下标被替换了。我想创建一个可以自动执行此操作的命令，语法如下
\replaceproduct{general term}{write first _ terms}{end with index at}
例如，对数字 N 进行质因数分解，如下所示
可以排版为
\replaceproduct{p_i^{\epsilon_i}}{3}{n}
我不确定这样的命令是否可行，并且我心中有疑虑（特别是关于命令如何知道索引变量 - 它可能必须是另一个参数，并且我不确定命令如何区分 \epsilon 中的 i 和 p_i 中的 i），但我对 LaTeX 不是很有经验。
答案1
我尝试expl3使用l3regex：
\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand\replaceproduct
{
O { i }
m
O { \cdots }
m
}
{
\seq_set_from_clist:Nn \l_tmpa_seq { #4 }
\seq_map_inline:Nn \l_tmpa_seq
{
\tl_set:Nn \l_tmpa_tl { #2 }
\tl_if_blank:nTF { ##1 }
{ #3 }
{
\regex_replace_all:nnN { #1 } { \cB\{ ##1 \cE\} } \l_tmpa_tl
\tl_use:N \l_tmpa_tl
}
}
}
\ExplSyntaxOff
\begin{document}
\(\replaceproduct{p_i^{\epsilon_i}}{1,2,3,{},n}\)
\end{document}
我使用的语法与你要求的略有不同。因为不会有也很多术语（我猜），那么我更喜欢这样：
\replaceproduct[<what-to-replace>]{<where-to-replace>}[<empty-item>]{<list-of-things>}
可选参数默认分别为i和\cdots。你可以使用以下方式排版：
\( \replaceproduct{p_i^{\epsilon_i}}{1,2,3,{},n} \)
此宏将遍历 ，<list-of-things>并将<what-to-replace>中找到的每个 替换<where-to-replace>为 中的一个项<list-of-things>。如果它找到{}，则改用<empty-item>。
编辑：
使用您要求的语法：
\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand\replaceproduct
{
O { i }
m
m
O { \cdots }
m
}
{
\int_zero:N \l_tmpa_int
\seq_set_from_clist:Nn \l_tmpa_seq { #5 }
\int_do_until:nNnn { \l_tmpa_int } = { #3 }
{
\int_incr:N \l_tmpa_int
\tl_set:Nn \l_tmpa_tl { #2 }
\regex_replace_all:nnN { #1 } { \cB\{ \c { \int_use:N } \c { \l_tmpa_int } \cE\} } \l_tmpa_tl
\tl_use:N \l_tmpa_tl
}
#4
\tl_set:Nn \l_tmpa_tl { #2 }
\regex_replace_all:nnN { #1 } { \cB\{ #5 \cE\} } \l_tmpa_tl
\tl_use:N \l_tmpa_tl
}
\ExplSyntaxOff
\begin{document}
\( \replaceproduct{p_i^{\epsilon_i}}{3}{n} \)
\end{document}
使用方式：
\replaceproduct[<what-to-replace>]{<where-to-replace>}{<from-one-to->}[<dots-thingy>]{<last-item>}
答案2
一些有趣的expl3技巧：
\documentclass{article}
\usepackage{amsmath}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\replaceproduct}{mmmm}
{% #1 = main terms
% #2 = exponent
% #3 = first terms
% #4 = last term
\int_step_inline:nn { #3 } { #1\sb{##1}^{#2\sb{##1}} }
\cdots
#1\sb{#4}^{#2\sb{#4}}
}
\NewDocumentCommand{\rp}{O{i}mmm}
{% #1 = item to substitute
% #2 = main terms
% #3 = first terms
% #4 = last term
\group_begin:
\tl_set:Nn \l__cid_rp_term_tl { #2 }
\regex_replace_all:nnN { #1 } { \cB\{\cP\#1\cE\} } \l__cid_rp_term_tl
\cs_set:NV \__cid_rp_term:n \l__cid_rp_term_tl
\int_step_function:nN { #3 } \__cid_rp_term:n
\cdots
\__cid_rp_term:n { #4 }
\group_end:
}
\tl_new:N \l__cid_rp_term_tl
\cs_generate_variant:Nn \cs_set:Nn { NV }
\ExplSyntaxOff
\begin{document}
\begin{gather}
N = \replaceproduct{p}{\varepsilon}{3}{m} = \replaceproduct{q}{\eta}{3}{n}
\\
N = \rp{p_i^{\varepsilon_i}}{3}{m} = \rp[j]{q_j^{\eta_j}}{3}{m}
\end{gather}
\end{document}
我发现第一个宏更容易输入。在第二个宏中，可选参数是要替换的虚拟变量，第二个实例j仅用作示例。
第二个宏是如何工作的？正则表达式部分将虚拟变量更改为#1；然后将标记列表作为替换文本传递\__cid_rp_term:n，而替换文本又用于\int_step_function:nN，它将执行从 1 到第二个参数中所述的情况。然后\cdots是最后一个案例。
答案3
这应该可以做到：
\newcommand{\replaceproduct}[4]{%
\saveexploremode%
\exploregroups%
\foreach \i in {1,...,#2}{\StrSubstitute{#1}{#3}{\i}} \ldots \StrSubstitute{#1}{#3}{#4}%
\restoreexploremode%
}
你必须使用pgffor和xstring包才能使其工作
使用示例：
\replaceproduct{p_i^{\epsilon_z}}{5}{z}{n}
第一个参数是通用术语，后跟重复次数，后跟索引占位符（必须是通用术语内的唯一字符序列），最后跟最终索引。
答案4
\documentclass{article}
\makeatletter
%%=============================================================================
%% Paraphernalia:
%% \UD@firstoftwo, \UD@secondoftwo,
%% \UD@PassFirstToSecond, \UD@Exchange, \UD@removespace
%% \UD@CheckWhetherNull, \UD@CheckWhetherBrace,
%% \UD@CheckWhetherLeadingSpace, \UD@ExtractFirstArg
%%=============================================================================
\newcommand\UD@firstoftwo[2]{#1}%
\newcommand\UD@secondoftwo[2]{#2}%
\newcommand\UD@PassFirstToSecond[2]{#2{#1}}%
\newcommand\UD@Exchange[2]{#2#1}%
\newcommand\UD@removespace{}\UD@firstoftwo{\def\UD@removespace}{} {}%
%%-----------------------------------------------------------------------------
%% Check whether argument is empty:
%%.............................................................................
%% \UD@CheckWhetherNull{<Argument which is to be checked>}%
%% {<Tokens to be delivered in case that argument
%% which is to be checked is empty>}%
%% {<Tokens to be delivered in case that argument
%% which is to be checked is not empty>}%
%%
%% The gist of this macro comes from Robert R. Schneck's \ifempty-macro:
%% <https://groups.google.com/forum/#!original/comp.text.tex/kuOEIQIrElc/lUg37FmhA74J>
\newcommand\UD@CheckWhetherNull[1]{%
\romannumeral0\expandafter\UD@secondoftwo\string{\expandafter
\UD@secondoftwo\expandafter{\expandafter{\string#1}\expandafter
\UD@secondoftwo\string}\expandafter\UD@firstoftwo\expandafter{\expandafter
\UD@secondoftwo\string}\expandafter\expandafter\UD@firstoftwo{ }{}%
\UD@secondoftwo}{\expandafter\expandafter\UD@firstoftwo{ }{}\UD@firstoftwo}%
}%
%%-----------------------------------------------------------------------------
%% Check whether argument's first token is a catcode-1-character
%%.............................................................................
%% \UD@CheckWhetherBrace{<Argument which is to be checked>}%
%% {<Tokens to be delivered in case that argument
%% which is to be checked has leading
%% catcode-1-token>}%
%% {<Tokens to be delivered in case that argument
%% which is to be checked has no leading
%% catcode-1-token>}%
\newcommand\UD@CheckWhetherBrace[1]{%
\romannumeral0\expandafter\UD@secondoftwo\expandafter{\expandafter{%
\string#1.}\expandafter\UD@firstoftwo\expandafter{\expandafter
\UD@secondoftwo\string}\expandafter\expandafter\UD@firstoftwo{ }{}%
\UD@firstoftwo}{\expandafter\expandafter\UD@firstoftwo{ }{}\UD@secondoftwo}%
}%
%%-----------------------------------------------------------------------------
%% Check whether brace-balanced argument starts with a space-token
%%.............................................................................
%% \UD@CheckWhetherLeadingSpace{<Argument which is to be checked>}%
%% {<Tokens to be delivered in case <argument
%% which is to be checked>'s 1st token is a
%% space-token>}%
%% {<Tokens to be delivered in case <argument
%% which is to be checked>'s 1st token is not
%% a space-token>}%
\newcommand\UD@CheckWhetherLeadingSpace[1]{%
\romannumeral0\UD@CheckWhetherNull{#1}%
{\expandafter\expandafter\UD@firstoftwo{ }{}\UD@secondoftwo}%
{\expandafter\UD@secondoftwo\string{\UD@CheckWhetherLeadingSpaceB.#1 }{}}%
}%
\newcommand\UD@CheckWhetherLeadingSpaceB{}%
\long\def\UD@CheckWhetherLeadingSpaceB#1 {%
\expandafter\UD@CheckWhetherNull\expandafter{\UD@secondoftwo#1{}}%
{\UD@Exchange{\UD@firstoftwo}}{\UD@Exchange{\UD@secondoftwo}}%
{\UD@Exchange{ }{\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter}\expandafter\expandafter
\expandafter}\expandafter\UD@secondoftwo\expandafter{\string}%
}%
%%-----------------------------------------------------------------------------
%% Extract first inner undelimited argument:
%%
%% \UD@ExtractFirstArg{ABCDE} yields {A}
%%
%% \UD@ExtractFirstArg{{AB}CDE} yields {AB}
%%.............................................................................
\newcommand\UD@RemoveTillUD@SelDOm{}%
\long\def\UD@RemoveTillUD@SelDOm#1#2\UD@SelDOm{{#1}}%
\newcommand\UD@ExtractFirstArg[1]{%
\romannumeral0%
\UD@ExtractFirstArgLoop{#1\UD@SelDOm}%
}%
\newcommand\UD@ExtractFirstArgLoop[1]{%
\expandafter\UD@CheckWhetherNull\expandafter{\UD@firstoftwo{}#1}%
{ #1}%
{\expandafter\UD@ExtractFirstArgLoop\expandafter{\UD@RemoveTillUD@SelDOm#1}}%
}%
%%=============================================================================
%% \DefineReplacementMacro{<replacement-macro>}%
%% {<internal helper-macro>}%
%% {<item to replace>}%
%%
%% defines <replacement-macro> to fetch two arguments,
%% #1 = <replacement for item to replace>
%% #2 = <token sequence with item to replace>
%% , and -- after two expansion-steps to deliver:
%% <token sequence with all instances of <item to replace> replaced
%% by <replacement for item to replace>. >
%%
%% Internally an <internal helper-macro> is needed.
%%
%% (!!! <replacement-macro> does also replace all pairs of matching
%% explicit character tokens of catcode 1/2 by matching braces!!!)
%%-----------------------------------------------------------------------------
\newcommand\DefineReplacementMacro[3]{%
\newcommand#2{}\long\def#2##1#3{}%
\newcommand#1[2]{%
\romannumeral0\UD@ReplaceAllLoop{##2}{##1}{}{#2}{#3}%
}%
}%
\newcommand\UD@ReplaceAllLoop[5]{%
\UD@CheckWhetherNull{#1}{ #3}{%
\UD@CheckWhetherLeadingSpace{#1}{%
\expandafter\UD@ReplaceAllLoop
\expandafter{\UD@removespace#1}{#2}{#3 }{#4}{#5}%
}{%
\UD@CheckWhetherBrace{#1}{%
\expandafter\expandafter\expandafter\UD@PassFirstToSecond
\expandafter\expandafter\expandafter{%
\expandafter\UD@PassFirstToSecond\expandafter{%
\romannumeral0\expandafter\UD@ReplaceAllLoop
\romannumeral0\UD@ExtractFirstArgLoop{#1\UD@SelDOm}{#2}{}{#4}{#5}%
}{#3}}%
{\expandafter\UD@ReplaceAllLoop\expandafter{\UD@firstoftwo{}#1}{#2}}%
{#4}{#5}%
}{%
\expandafter\UD@CheckWhetherNoReplacement
\romannumeral0\UD@ExtractFirstArgLoop{#1\UD@SelDOm}{#1}{#2}{#3}{#4}{#5}%
}%
}%
}%
}%
\newcommand\UD@CheckWhetherNoReplacement[6]{%
\expandafter\UD@CheckWhetherNull\expandafter{#5#1#6}%
{%
\expandafter\UD@ReplaceAllLoop
\expandafter{\UD@firstoftwo{}#2}{#3}{#4#1}{#5}{#6}%
}{%
\expandafter\UD@ReplaceAllLoop
\expandafter{\UD@firstoftwo{}#2}{#3}{#4#3}{#5}{#6}%
}%
}%
%%=============================================================================
%% \UD@ReplaceAlli -- Replace all "i" in undelimited Argument:
%%
%% \UD@ReplaceAlli{<replacement for i>}{<token sequence with i>}
%% yields <token sequence with all i replaced by replacement for i>
%%
%% <replacement for i> may contain i.
%%
%% (This routine does also replace all pairs of matching explicit
%% character tokens of catcode 1/2 by matching braces!!!)
%%
%% The letter "i" as item to replace is hard-coded.
%% You cannot replace öetters other than I with this macro.
%%.............................................................................
\DefineReplacementMacro{\UD@ReplaceAlli}{\UD@gobbletoi}{i}%
%%
%%=============================================================================
%% \replaceiandreplicate{<term with i>}%
%% {<loop-start-index>}%
%% {<loop-end-index>}%
%% {<separator>}%
%% {<end index>}
%%
%% e.g.,
%%
%% \replaceiandreplicate{p_i^{\epsilon_i}}{1}{3}{\cdots}{n}
%%.............................................................................
\newcommand\replaceiandreplicate[5]{%
\romannumeral0\expandafter\expandafter
\expandafter \UD@Exchange
\expandafter\expandafter
\expandafter{%
\UD@ReplaceAlli{#5}{#1}%
}{%
\replaceiandreplicateloop{#3}{#2}{#1}#4%
}%
}%
\newcommand\replaceiandreplicateloop[3]{%
\ifnum#1<#2 %
\expandafter\UD@firstoftwo
\else
\expandafter\UD@secondoftwo
\fi
{ }{%
\expandafter\expandafter
\expandafter \UD@Exchange
\expandafter\expandafter
\expandafter{%
\UD@ReplaceAlli{#1}{#3}%
}{%
\expandafter\replaceiandreplicateloop
\expandafter{\number\numexpr\number#1-1\relax}{#2}{#3}%
}%
}%
}%
\makeatother
\parindent=0ex
\begin{document}
\begin{verbatim}
$\replaceiandreplicate{p_{i}^{\epsilon_{i}}}{1}{3}{\cdots}{n}$
\end{verbatim}
yields:\bigskip
$\replaceiandreplicate{p_{i}^{\epsilon_{i}}}{1}{3}{\cdots}{n}$
\bigskip\hrule
\begin{verbatim}
$\csname @gobble%
\expandafter\expandafter
\expandafter\endcsname
\replaceiandreplicate{\cdot p_{i}^{\epsilon_{i}}}{-3}{5}{\cdot\;\cdots\;}{n}$
\end{verbatim}
yields:\bigskip
$\csname @gobble%
\expandafter\expandafter
\expandafter\endcsname
\replaceiandreplicate{\cdot p_{i}^{\epsilon_{i}}}{-3}{5}{\cdot\;\cdots\;}{n}$
\bigskip\hrule
\begin{verbatim}
\def\sgn#1{\ifnum0<\number\ifx-#1\else-0#1\fi\else+\fi#1}
$\csname @gobble%
\expandafter\expandafter
\expandafter\endcsname
\replaceiandreplicate{\cdot p_{k\sgn{i}}^{\epsilon_{i}}}{-3}{5}{\cdot\;\cdots\;}{n}$
\end{verbatim}
yields:\bigskip
\def\sgn#1{\ifnum0<\number\ifx-#1\else-0#1\fi\else+\fi#1}
$\csname @gobble%
\expandafter\expandafter
\expandafter\endcsname
\replaceiandreplicate{\cdot p_{k\sgn{i}}^{\epsilon_{i}}}{-3}{5}{\cdot\;\cdots\;}{n}$
\end{document}
