I would like to place a subscript under two summation signs in a fraction, in an equation. The code showed works when it is not in a fraction, but as soon as I use it in a fraction the subscript is placed after the two summation signs, instead of under the two summation signs.

\begin{equation} \frac{{\sum\sum\limits}_{i \neq j}
    \sum\limits_{x}\sum\limits_{y}[\pi_{x(i),y(j)} -
    \pi_{x(i)}\pi_{y(j)}]} {\sigma^2_X} 

Does anyone know how to solve this?

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    – user31729
    Jan 28, 2015 at 13:02

2 Answers 2


You need to enclose the two summation symbols in \mathop{} and then place \limits after that.


  \frac{\mathop{\sum\sum}\limits_{i \neq j}
    \sum\limits_{x}\sum\limits_{y}[\pi_{x(i),y(j)} -


enter image description here

  • +1. Also, I'd add the new operator double sum \DeclareMathOperator*{\dsum}{\sum\sum}
    – Sigur
    Jan 28, 2015 at 13:01
  • 3
    @Sigur True, even thought I would only declare a new operator if I were to use this construct multiple times. Jan 28, 2015 at 13:06

If you use lualatex, you can place the \limits outside of the braces:

{\sum\sum}\limits_{i\neq j}

However, this will throw an error if compiled with pdflatex or xelatex, then you need a \mathop:

\mathop{\sum\sum}\limits_{i\neq j}

If you need this more often, you can define a new mathoperator (needs amsmath), if you use the starred Version, the default is the use of \limits.


If you are inside a \frac, displaymode is turned of, you can switch it back on:

  \frac{\displaystyle \ssum_{i\neq j}}{2}
  • It does not work. Limit controls must follow a math operator. ...} {\sum\sum}\limits
    – Sigur
    Jan 28, 2015 at 13:04
  • This won't work. ! Limit controls must follow a math operator. Please improve your answer. Jan 28, 2015 at 13:04
  • i compiled it! With lualatex using mathtools and unicode-math
    – MaxNoe
    Jan 28, 2015 at 13:05
  • @MaxNoe, in that case, it works.
    – Sigur
    Jan 28, 2015 at 13:08
  • 3
    @MaxNoe Aha! You found another tex vs. luatex incompatibility. Jan 28, 2015 at 13:08

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