[Tex/LaTex] Why no space between operators in super and subscript

defaultoperator-space

By default operator space didn't come for super and subscripts which is correct in general. Refer the below code:

\documentclass{book}

\begin{document}

\[
a+b\sum+\int_{a+b\quad a=b}
\]

\end{document}

But any one can explain why this was fixed? I need to know this in detail…

Best Answer

By default binary operators such as + get a \medmuskip space either side, and relations such as = get \thickmuskip but this additional space is not added in scriptstyle and scriptscriptstyle settings. This is not configurable by TeX macros, it is built into the TeX sources as part of its math layout.

A \quad is just defined to be \hskip1em so it is not really a math-aware space it is 1em in the text font current before the math started. You can use \nonscript\quad if you really need to use a quad that vanishes in subscripts.

\documentclass{book}

\begin{document}

\[
a+b\sum+\int_{a+b\nonscript\quad a=b}
\]

\end{document}

or use a math space such as \: that adjusts to the subscript font size:

\documentclass{book}

\begin{document}

\[
a+b\sum+\int_{a+b\: a=b}
\]

\end{document}

\: is \mskip\medmuskip and skips specified in mu units are relative to the current math style.

Related Solutions

[Tex/LaTex] the right space between a math operator and its subscript

\documentclass[fleqn]{article}
\usepackage{amsmath, amssymb}
\DeclareMathOperator{\Pm}{\mathcal{P}}
\showoutput
\begin{document}
\begin{align*}
    &\mathcal{P}_{\mathrm{ext}}(H) \\
    &\operatorname{\mathcal P}_{\mathrm{ext}}(H) \\
    &\Pm_{\mathrm{ext}}(H)\\
    &\mathop{\mathcal{P}_{\mathrm{ext}}}(H) 
\end{align*}


a $\log x$


a ${}\log x$

\end{document}

The specific example makes the answer a bit trickier than it would otherwise have been. I would say that the most logical markup would be \mathop{\mathcal{P}_{\mathrm{ext}}} as you want the subscripted term itself act as a \mathop.

However the reason that you see different spacing here is because you are on the right hand side of an alignment where implicitly the expression is prefixed by {} so you are getting a thin space from the \mathop to separate it from the (invisible) preceding term. So it is like the second \log example I added to the example here/ So why in the vast majority of cases the \mathop spacing for \log is the right thing the extra space here is probably not right and should be removed by \! or by using a form that does not give a \mathop, eg {\Pm}

[Tex/LaTex] Why is Latin Modern the default font with xelatex and lualatex

Latin Modern is closely related to Computer Modern (the other main contender being Computer Modern Unicode) This family of fonts is strongly tied to TeX's history.

Until very recently (2016 release) xelatex and lualatex defaulted, like pdflatex, to 7-bit cmr10.tfm so using the OpenType Latin Modern is already a big increase in coverage from that.

When people are experimenting with switching from classic TeX to luatex or xetex it is helpful to have a default setup that produces a broadly similar document, and that means that Latin Modern or Computer Modern Unicode are the only really viable defaults.

The default also needs to be a font distributed in major TeX distributions so that it can be reliably expected to be available on all the platforms where TeX is used.