I am using the latest version of LyX and I am having trouble getting the limits to work at all. Ideally, I'd like to be able to place the summation limits above and below the sigma. However, at this point, I would settle for the less-pleasing-to-my-eyes variant of having the limits in the northeast and southeast corners of the symbol. However, try as I might, LyX does not want to place the limits anywhere. The "Change Limits Type" whose use I have seen recommended in various forums remains greyed out no matter what I do and the documentation does not provide any information I have yet found on how the process is even supposed to work in theory. On an admittedly editorial note, I am beginning to feel LyX is extremely lacking in documentation, which is unfortunate as I think it otherwise is a great application. Anyway, if Someone could point me in the direction of how to resolve this issue, I'd greatly appreciate it.

# [Tex/LaTex] LyX and Summation

lyxmath-operators

#### Related Solutions

You want to use `\bigoplus`

instead of `\oplus`

.

I've never seen concatenation done that way. Addition and XOR are commutative operations so it makes sense to sum over a set (or take the exclusive OR of a set). Concatenation is not like that. I think I would explicitly write out the concatenation. That said, you can use `\bigparallel`

from the `stmaryrd`

package.

```
\documentclass{article}
\usepackage{amsmath}
\usepackage{stmaryrd}
\newcommand*\concat{\mathbin{\|}}
\begin{document}
\[x_1\concat x_2\concat\dotsb\concat x_n\]
\[\bigparallel_{i=1}^n x_i\]
\end{document}
```

You could create your own symbol using `ooalign`

as demonstrated in

- What is the command for a sum symbol superimposed on an integral sign?
- \subseteq + \circ as a single symbol ("open subset") which contains a great tutorial on
`ooalign`

The subtle thing in the code below is that I've used a `\phantom{sum}`

in the `displaystyle`

version to make sure that limits of the `sum`

are displayed correctly. Without it, you loose the correct display of the upper limit.

If the circles aren't exactly where you want them, you can move them around by playing with the numbers in the code.

```
\documentclass{article}
\usepackage{amsmath}
\usepackage{graphicx}
% a new command to draw the little circle
\newcommand{\smallcirc}[1]{\scalebox{#1}{$\circ$}}
\DeclareMathOperator*{\SumCircles}{%
\mathchoice%
{\ooalign{\phantom{$\displaystyle\sum$}\cr\hidewidth\raisebox{1.2\height}{$\mkern22mu\smallcirc{0.7}$}\hidewidth\cr%
\raisebox{-0.7\height}{$\mkern22mu\smallcirc{0.7}$}\cr
\hidewidth$\displaystyle\sum$}}
{\ooalign{$\textstyle\sum$\cr%
\hidewidth\raisebox{1.9\height}{$\mkern16mu\smallcirc{0.4}$}\hidewidth\cr
\hidewidth\raisebox{-.3\height}{$\mkern16mu\smallcirc{0.4}$}\hidewidth\cr}}
{\ooalign{\raisebox{0\height}{\scalebox{.6}{$\scriptstyle\sum$}}\cr%
\hidewidth\raisebox{1.6\height}{$\mkern7.5mu\smallcirc{0.2}$}\hidewidth\cr
\hidewidth\raisebox{-0.2\height}{$\mkern7.5mu\smallcirc{0.2}$}\hidewidth\cr}}
{\ooalign{\raisebox{.2\height}{\scalebox{.6}{$\scriptstyle\sum$}}\cr%
\hidewidth\raisebox{2.2\height}{$\mkern7.5mu\smallcirc{0.2}$}\hidewidth\cr
\hidewidth\raisebox{0.4\height}{$\mkern7.5mu\smallcirc{0.2}$}\hidewidth\cr}}
}
\begin{document}
$\SumCircles_{\SumCircles} \displaystyle\SumCircles$
\[
\SumCircles_{n=1}^\infty
\sum_{n=1}^\infty
\]
\end{document}
```

## Best Answer

The problem might be that you first have to type at least one of lower or upper limit, or need to place the cursor at the

`\sum`

symbol to be able to change the limit type.`\sum`

, hit space.`_`

as used for indices in math mode and type the lower limit (for example "i=1"), hit space.`^`

as used for exponents in math mode and type the upper limit (for example "10"), hit space.There is some documentation, which is integrated in LyX. You can find basic information about math mode in "Help > Tutorial" in Chapter 4 "Using Math" and advanced information in "Help > Math" in Chapter 10 "Operators".