20

I want to get the following:

What I want to have

I tried the following

\[
   a(i,k) \leftarrow 
   \min\Big\{0, r(k,k) + \sum_{i^{'} | i^{'}\notin \{i,k\}}\max\{0, r(i{'},k)\}\Big\}
\]

and got

What I got

How can I make the part under the summation extend to left and right without making a space between plus and max as in the first figure?

  • 2
    Such a formula should be between \[ and \], rather than $\displaystyle and $: if set inline it will spoil the appearance of the page. – egreg Jan 12 '13 at 22:29
  • Thanks. But even within the brackets (no inline), I can't remove the extra spaces. – petrichor Jan 12 '13 at 22:35
  • By the way, I noticed that I forgot the extra bracket at the end, I will correct it. – petrichor Jan 12 '13 at 22:36
22

Apart from \mathclap{…}, mathtools provides a command specifically set for these situations: \smashoperator{…}. Which is, more or less, like putting \mathclap{…} in both (sub and super scripts). Taking @tohecz advice about a'|a', your code will be like

\documentclass{article}
\usepackage{mathtools}

\begin{document}
\[
   a(i,k) \gets \min\Bigl\{ 0, r(k,k) + \smashoperator{\sum_{i'\notin\{i,k\}}} \max\{0, r(i',k)\} \Bigr\}
\]
\end{document}

Which will be like all the other answers. Moreover, that command has an optional argument: lr, default one, will smash both sides; r only smash the right; and l will smash the left. In the examples I will add some text over the operator so you can see how it works (it smashes both).

enter image description here

13

You can load the package mathtools and write:

\[
   a(i,k) \leftarrow 
   \min\Big\{0, r(k,k) + \sum_{\mathclap{i'\mid i'\notin \{i,k\}}}
   \max\{0, r(i',k)\}\Big\}
\]

However, I always prefer some space left around such sum:

enter image description here

\[
   a(i,k) \leftarrow 
   \min\Big\{0, r(k,k) + \;\sum_{\mathclap{i'\mid i'\notin \{i,k\}}}\;
   \max\{0, r(i',k)\}\Big\}
\]

As well:

  • Notice that the syntax for the prime is neither i^{'} nor i{'}. It is i'.

  • It might be better to use \mid instead of |. Here, the result is the same, but the symbol | has four different meanings (relation, operator, open delim, close delim), and it is a good practice to always use one of \mid, \vert, \lvert, \rvert.

  • In my opinion, \sum_{i|i\notin X} is redundant, you can write just \sum_{i\notin X}. It is a common practice that summation is over the very first variable in the sum's index.

  • Typing \Bigl\{ ... \Bigr\} instead of \Big\{...\Big\} costs two keystrokes more, and you keep the sematics correctly, as well in some cases it is necessary (absolute value |.|, reverse-bracket open intervals ].[ etc.)

  • You can make the braces after \max bigger, it doesn't cost any space and it increases readibility and visual appearance.

enter image description here

\[
   a(i,k) \leftarrow 
   \min\Bigl\{0, r(k,k) + \;\sum_{\mathclap{i'\notin \{i,k\}}}\;
   \max\bigl\{0, r(i{'},k)\bigr\}\Bigr\}
\]
  • I'd prefer \mid instead of |; the result here is the same, but it reminds to use it also in text or display style. – egreg Jan 12 '13 at 22:43
  • I think you should talk about \smashoperator{…} which was designed for this (i.e., it helps if you have to smash the subscript and the superscript). – Manuel Jan 12 '13 at 23:01
  • @Manuel You can post it as a seperate answer I think. I haven't known it even exists so I'll be glad to see an example of its usage. – yo' Jan 12 '13 at 23:03
7

You can use \mathclap{....} from mathtools:

\documentclass{article}
\usepackage{mathtools}
%
\begin{document}
 \[
   a(i,k) \leftarrow 
   \min\Big\{0, r(k,k) + \sum_{\mathclap{i^{'} | i^{'}\notin \{i,k\}}}\max\{0, r(i{'},k)\}\Big\}
\]
\end{document}

enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.