Summation with system of aligned equations as lower limit

Question

I'm trying to write a summation with a system of aligned equations as lower limit. To do that I wrote:

$$
I_{P+AH, a} = \sum
_{\begin{empheq}[left=\empheqlbrace]{align*}
 &\tau_i \text{ ATTIVO} \\
 &d_i < d_{a_i} 
\end{empheq}}
c
$$

but Texmaker gives me an error (bad math environment). How can I do it?

Hi @Mico I need only to align the two equations of the system in a way that d_i will be aligned with tau_i — Gennaro Arguzzi, Apr 04 '21 at 16:50

Vincent · Answer 1 · 2021-04-04T16:55:26.040

4

You're getting an error because you try to use empheq inside another math environment, which doesn't make sense. However, you don't really need empheq for that, you can just use substack surrounded with \left\{ ... \right.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
I_{P+AH, a} = \sum_{\left\{ \substack{
     \tau_i \text{ ATTIVO} \\
     d_i < d_{a_i}
} \right.}
c
\]
\end{document}

If you want the conditions to be left-aligned, you can follow @daleif's suggestion and use a subarray environment instead of \substack.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
I_{P+AH, a} = \sum_{\left\{ \begin{subarray}{l}
     \tau_i \text{ ATTIVO} \\
     d_i < d_{a_i}
\end{subarray} \right.}
c
\]
\end{document}

Also, it is not related to your problem, but you should not use $$...$$, you should use \[...\] instead.

edited Apr 04 '21 at 16:55

answered Apr 04 '21 at 16:44

Vincent

20,157

Hello @Vincent, thank you for your help. How can I shift the second equation to the left side so that the d_i is aligned with tau_i? – Gennaro Arguzzi Apr 04 '21 at 16:46
@GennaroArguzzi \substack is basically the same as \begin{subarray}{c} ... \end{subarray} so use that instead with {l} instead of {c} – daleif Apr 04 '21 at 16:50
Hello @daleif can you post an example of the requirement I asked to Vincent please? – Gennaro Arguzzi Apr 04 '21 at 16:53
@GennaroArguzzi that is exactly what I already wrote. And what Vincent changed the code to. – daleif Apr 04 '21 at 16:55
1

@GennaroArguzzi I updated my answer with a second solution. – Vincent Apr 04 '21 at 16:55
Thank you very much @Vincent – Gennaro Arguzzi Apr 04 '21 at 16:56
The (lack of) spacing around the < symbol in the second row below \sum doesn't look good. – Mico Apr 04 '21 at 16:58

Mico · Accepted Answer · 2021-04-04T17:09:56.453

4

Here's are array-based and smallmatrix*-based solutions. (Many thanks to @daleif for suggesting the second solution type.)

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\[
I_{P+AH, a} 
= \sum_{
  \Bigl\{ \begin{array}{@{}l@{}}
             \tau_i \textsc{ attivo} \\
             d_i < d_{a_i} 
          \end{array} }
c 
= \sum_{
  \bigl\{ \begin{smallmatrix*}[l]
             \tau_i \text{ \scshape attivo} \\
             d_i\, <\, d_{a_i}
          \end{smallmatrix*}}
c
\]
\end{document}

edited Apr 04 '21 at 17:09

answered Apr 04 '21 at 16:56

Mico

506,678

I appreciate your answer. – Gennaro Arguzzi Apr 04 '21 at 16:57
IMO this just looks too large. Would smallmatrix* be better? – daleif Apr 04 '21 at 16:59
1

@daleif - Many thanks for this great suggestion. I've incorporated it in an update to my answer. – Mico Apr 04 '21 at 17:10

Summation with system of aligned equations as lower limit

2 Answers2