# Display inline sums

I am writing my thesis and I have some sums which are inline, and others which are part of equations.

My questions is: is there a convention, an unwritten rule about how inline equations should be displayed? Which of the following is the "right" one for this kind of situation?

• $T=\{\sum\nolimits_{i:e_{i} \in S_{j}} y_{i} = w_{j}\}$
• $T=\{\displaystyle\sum\limits_{i:e_{i} \in S_{j}} y_{i} = w_{j}\}$

In a book I have seen that all the inline sums are written with the first code, while the ones from equations with the second. Is this the correct way?

• This may solicit primarily opinion-based answers and is not really a good fit for Stack Exchange. – Werner Jun 25 '14 at 22:44
• The second will make the line too high and deep, producing bad white stripes on the page; moreover the braces are too small. In the first \nolimits is redundant and Probes should really be \operatorname{Probes} or \mathit{Probes}. – egreg Jun 25 '14 at 22:49
• @Werner: I'm sorry it's not a good fit, but I just wanted to know if there was a rule which said how the sums should be displayed; @egreg: Sorry, but Probes shouldn't be there; I forgot to erase it, but I will edit my question. – Jessy09 Jun 25 '14 at 22:57

## 2 Answers

It is the correct way, because inline formulas shouldn't be too high. Theoretically, the distance between lines should be constant, which is impossible, when formulas are in the display style.

• actually, the "rule" is not unwritten. books for math compositors (originally for metal composition) do specify the "nolimits" convention for in-line sums and friends. for more "contemporary" guidance, see Mathematics into Type, page 81. – barbara beeton Jun 26 '14 at 17:20

A solution to have \sum\limits for in line maths without increasing the interline spacing can be to :

1) slighly increase the value of \baselinestretch, with the setspace package, say \setspace{1.1}.

2) use the medium sized math macros from the nccmath package (\medop\sum\limits).

3) use it moderately.

It's not so much the problem of sums, I must say, but I find the difference between textstyle and displaystyle fractions a startling contrast, and I usually prefer to use the \mfrac command.