1

Why is it that

\[
  f\langle s,t \rangle = \sum_\substack{v,w \in E \\ v \in S, w \in T}}f(v,w) \\    
\]

compiles for me, despite the extra }, but

\[
  f\langle s,t \rangle = \sum_\substack{v,w \in E \\ v \in S, w \in T}f(v,w) \\    
\]

does not?

Edit: amsmath 2000/07/18 v2.13, pdfTeX, Version 3.1415926-2.4-1.40.13 (TeX Live 2012/W32TeX) (format=pdflatex 2013.3.3)

1 Answer 1

4

Please always post complete documents:

I get an error on both lines:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\[
  f\langle s,t \rangle = \sum_\substack{v,w \in E \\ v \in S, w \in T}}f(v,w)    \\
\]

compiles for me, despite the extra \}, but

\[
  f\langle s,t \rangle = \sum_\substack{v,w \in E \\ v \in S, w \in T}f(v,w) \\    
\]

does not?

\end{document}

Produces

! Missing { inserted.
<to be read again> 
                   \vcenter 
l.8 ...um_\substack{v,w \in E \\ v \in S, w \in T}
                                                  }f(v,w) \\
? 
(/usr/local/texlive/2012/texmf-dist/tex/latex/base/omscmr.fd)
! Missing { inserted.
<to be read again> 
                   \vcenter 
l.14 ...m_\substack{v,w \in E \\ v \in S, w \in T}
                                                  f(v,w) \\
? x
No pages of output.

with an error on lines 8 and 14.

The error is a missing { after the _

This produces no error:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\[
  f\langle s,t \rangle = \sum_{\substack{v,w \in E \\ v \in S, w \in T}}f(v,w)   
\]


\end{document}
2
  • I'll keep the complete documents thing in mind. Also, I was under the impression that one entity counted as the same, for example a_\mathrm{min} is valid. Why is this different? Commented Apr 9, 2013 at 13:20
  • @HameerAbbasi \mathrm is designed so that works (athough it is bad style:-) the {} are required but the expansion of \mathrm includes the brace. Compare A_\foo with \newcommand\foo{abcd} or with \newcommand\foo{{abcd}} one gets subscript a the other abcd Commented Apr 9, 2013 at 13:30

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