\eqref issues / ref and labelling issues in align environment

Question

@werner edited comment: Hi, okay, many thanks for your reply. That has resolved one of them but I am still having trouble with- I have uploaded a new screenshot, it should now be the first one- with referencing the $\lag$ label- I thought a line was defined by the \ splits, but , with the attached screenshot - (my apologies ignore the \nonumber after the \phi .. i have deleted this and what I am about to say still holds, and with \nonumber and \notag). As the code stands the reference works ok, but there's an extra number label in the equation, to me, anyway, at the moment my interpretation of the current code is that the \nonumber and \label are both within the same line, and so the referencing should not work, but it does. When I try moving the \nonumber to the other side of the \, it renders an error..many thanks in advance

I am sure sometimes \eqref is working and other times it isnt...I'm finding the same with $\ref{ } $ . I have tried without the dollar signs, with, using both of these ways to reference. And it seems totally hit and miss to when it's working and when it's not. I've tried to look if it is to do with where you label the equation, which line etc, when working in the align environment compared to the equation environment etc, but can not seem to spot anything consistent. I have attached screen-shots of instances where it has worked and where it hasn't. So, for example, in the first, second&third screen-shot it doesn't work and the screenshots show how I've labelled them in these instances (sorry in the second case it is not circled but shown above how I labelled it), in the fourth it works fine, and the screenshot below shows how I've labelled them for that one, final screenshot shows how I labelled the equation for the case of screen-shots 2 and 3 where it is referred to but does not work.

Welcome to TeX.SE! Do not show code in an image, we can not copy it and test it ... — Mensch, Dec 07 '21 at 16:58
\ref should not be in math mode so certainly without the $ but it is impossible to debug a screenshot, show a small complete example of your problem in a code block in the question, — David Carlisle, Dec 07 '21 at 17:02
Getting ??? on the first run after you add a \label is the expected output, you need to run latex again to resolve cross references. — David Carlisle, Dec 07 '21 at 17:04
Does this answer your question? Understanding how references and labels work — Teepeemm, Dec 07 '21 at 18:51
Especially the part "2. How many times do I have to compile?" — Teepeemm, Dec 07 '21 at 18:52

score 3 · Answer 1 · answered Dec 07 '21 at 19:18

The following replicates your issue - having a \label together with \notag (or \nonumber):

\documentclass{article}
\usepackage{amsmath}
\begin{document}
See~\eqref{eq:f_equals_g_a} and~\eqref{eq:f_equals_g_b}.
\begin{align}
  f(x) &= ax^2 + bx + c \label{eq:f_equals_g_a} \
       &= g(x) \notag\label{eq:f_equals_g_b}
\end{align}
\end{document}

\notag (or \nonumber) effectively negates the use of \label, making all the associated references undefined. This makes sense since there's no number to reference. To solve the issue, move the \label into a line within the align that has a number (therefore no \notag or \nonumber).

Hi, many thanks for your reply , it has helped one error but still having issues with the other- please see edited comment in the OP. thanks a lot ! — sars909, Dec 08 '21 at 16:39

\eqref issues / ref and labelling issues in align environment

1 Answers1