Simultaneous equations and separate labels

Question

Essentially I'm trying to obtain something like this (without the f(x) bit), but with custom labels, which I can't seem to do.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align*}
\begin{cases}
x+y &= 3 &&& \text{5} \\
x-y &= 1 &&& \text{6} \\
\end{cases}
\end{align*}

\end{document}

But it just doesn't work.

I additionally tried the numcases solution in the link, but it seems like I can't manually tag it.

Here is my attempt with the empheq package:

\documentclass[preview]{standalone}
\usepackage{amsmath,empheq}
\usepackage{cases}
\begin{document}

\begin{empheq}{align*} 
\begin{cases}
x+y &= 3 \tag{5} \\
x-y &= 1 \tag{6}
\end{cases}
\end{empheq}

\end{document}

The problem over here is that it shows only a (5) next to both the equations somewhere vertically in the center, not a (5) for one equation and a (6) for the other ;P

@gernot Unfortunately, I can't use tag in a numcases environment it seems.... — Skeleton Bow, Oct 30 '16 at 17:34
@Mico well, I really wanted it :) that's the reason I'm asking! — Skeleton Bow, Oct 30 '16 at 17:47
See empheq, AFAIR you can overwrite the eqn no using tag in that construction — daleif, Oct 30 '16 at 17:51
@daleif thanks for the suggestion, but I can't see anything that's related to tags… sorry, I'm quite new to this language — Skeleton Bow, Oct 30 '16 at 18:00
There is an example in the manual for that package that gives you a cases-like output with eqn numbers. Try to copy that example, when it works try overwriting the eqn number using \tag, I'm not at a pc so cannot do it for you. — daleif, Oct 30 '16 at 18:03
does this help: Separate labels in cases? it's possible to have nothing on the left preceding the brace; just leave the first argument empty {}. — barbara beeton, Oct 30 '16 at 18:22
@daleif Okay, I just tried that suggestion and it seems to give a custom tag, but it doesn't look like I can tag both equations in the braces. Thanks anyway for helping! — Skeleton Bow, Oct 30 '16 at 18:44
Why not? Please update your question with the code you have now — daleif, Oct 30 '16 at 18:46
@daleif Hey, I did it, but someone already answered it for me giving me an alternate way of doing it. So you don't need to look at my question. But thank you very, very much for trying to help. — Skeleton Bow, Oct 30 '16 at 18:53
That is not how the example goes in the manual. Remove the inner cases, and add the left brace via the extra optional option to empheq — daleif, Oct 30 '16 at 18:55
See the example code at the bottom of page 7 (result is on page 8), remove the right part. Note that tag overwrites also in non-starred align. — daleif, Oct 30 '16 at 18:59

score 3 · Accepted Answer · edited Apr 13 '17 at 12:35

3

try this:

\documentclass{article}
\usepackage{amsmath}
\usepackage{cases}

\begin{document}
\setcounter{equation}{4}
\begin{numcases}{}
 x+y = 3 \\
 x-y = 1
\end{numcases}
\end{document}

this is exactly what is provided by the examples in this question: Separate labels in cases, which is why i suggested it as a duplicate.

edited Apr 13 '17 at 12:35

Community

1

answered Oct 30 '16 at 18:49

barbara beeton

88,848

1

I'm sorry! I was playing around with the examples but I didn't get anywhere. I had no idea about the setcounter command! I also searched for it on that page, but couldn't see it there... – Skeleton Bow Oct 30 '16 at 18:51
I'd like to add the reason I was completely clueless about this. I never used the equation environment because I write in MathJax with $$ and use pandoc to convert it over (which is far from perfect), and I always used the tag command to number my equations, so I never had "official" equation counters anyway! That's why nothing was working for me. Thanks for helping me. – Skeleton Bow Oct 30 '16 at 18:56
@SkeletonBow -- your confusion is understandable, given your method of preparing input. however, it would have made the question more understandable if you'd included the information about that method in the question. – barbara beeton Oct 30 '16 at 21:30

Simultaneous equations and separate labels

1 Answers1