这个 MWE 展示了我遇到的问题：
\documentclass{article}
\usepackage{amsmath}
\usepackage{mathtools}
\begin{document}
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
\[
\sum_{\alpha \in \{a,b,c,d,e,f,g,h,i,j,k,\ell,m,n,o,p,q,r,s,t,u,v,w,x,y,z\}} 1 + \alpha + \alpha^2 + \alpha^3 + \alpha^4 + \alpha^5 + \alpha^6 + \alpha^7 + \alpha^8 + \alpha^9
\]
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
Using ``mathclap'':
\[
\sum_{\mathclap{\alpha \in \{a,b,c,d,e,f,g,h,i,j,k,\ell,m,n,o,p,q,r,s,t,u,v,w,x,y,z\}}} 1 + \alpha + \alpha^2 + \alpha^3 + \alpha^4 + \alpha^5 + \alpha^6 + \alpha^7 + \alpha^8 + \alpha^9
\]
\end{document}
问题：
我如何才能实现将字母总和向左移动（总和下标的顶部）直到它们与右边距右对齐的等效效果？总和及其下标不应从其当前左对齐位置移动。
答案1
如果我理解正确的话，那么 alphas ( 1 + \alpha + ...) 的总和应该向左移动以避免出现过多的\hbox警告：
\documentclass{article}
\usepackage{amsmath}
\begin{document}
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
\[
\sum_{\alpha \in \{a,b,c,d,e,f,g,h,i,j,k,\ell,m,n,o,p,q,r,s,t,u,v,w,x,y,z\}}
\hspace{0pt minus 12.2pt}% value taken from the overful \hbox message
1 + \alpha + \alpha^2 + \alpha^3 + \alpha^4 + \alpha^5 + \alpha^6 + \alpha^7 + \alpha^8 + \alpha^9
\]
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
\[
\sum_{\alpha \in \{a,b,c,d,e,f,g,h,i,j,k,\ell,m,n,o,p,q,r,s,t,u,v,w,x,y,z\}}
\hspace{0pt minus 1fil}% allows natural width for the spacing around plus operators
1 + \alpha + \alpha^2 + \alpha^3 + \alpha^4 + \alpha^5 + \alpha^6 + \alpha^7 + \alpha^8 + \alpha^9
\]
\end{document}
避免使用魔法数字
\documentclass{article}
\usepackage{amsmath}
\newsavebox\testbox
\begin{document}
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
\newcommand*{\alphasum}[1]{%
\sum_{\alpha \in \{a,b,c,d,e,f,g,h,i,j,k,\ell,m,n,o,p,q,r,s,t,u,v,w,x,y,z\}}
\hspace{0pt minus #1}
1 + \alpha + \alpha^2 + \alpha^3 + \alpha^4 + \alpha^5 + \alpha^6 + \alpha^7
}
\sbox\testbox{$\displaystyle\alphasum{0pt}$}%
\[
\ifdim\wd\testbox>\linewidth
\alphasum{\dimexpr\wd\testbox-\linewidth}%
\else
\alphasum{0pt}%
\fi
\]
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
This is a really long line of text to show where the margins of the page are.
\[
\sum_{\alpha \in \{a,b,c,d,e,f,g,h,i,j,k,\ell,m,n,o,p,q,r,s,t,u,v,w,x,y,z\}}
\hspace{0pt minus 1fil}
1 + \alpha + \alpha^2 + \alpha^3 + \alpha^4 + \alpha^5 + \alpha^6 + \alpha^7
\]
\end{document}
把事情简单化
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
\sum_{\alpha \in \{a,b,c,\dots, z\}}
\hspace{0pt minus 1fil}
1 + \alpha + \alpha^2 + \alpha^3 + \dots + \alpha^9
\]
\end{document}
答案2
+1，Heiko 的回答，特别是他关于保持简单。
我实际上会重写你的表达以使用本地定义
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
\sum_{\alpha \in S}
1 + \alpha + \alpha^2 + \alpha^3 + \dots + \alpha^9
\]
where
\[
S=\{a,b,c,\dots, z\}
\]
\end{document}
答案3
您可以将 smashoperator 与 \include{mathtools} 一起使用
\smashoperator[r]{\sum\limits_{parangaricutirimicuaro}} f(x)。
我最近在一篇文章中使用了它，效果非常好。希望它能有所帮助。