# 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, 2014 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}. Jun 25, 2014 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. Jun 25, 2014 at 22:57

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. Jun 26, 2014 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.