# internal error in breqn package with dseries/dmath* pair

As an experiment, I took some equations that I'd manually split using aligned like so:

\label{eqn:fourierSeries:30} \begin{aligned} \int_a^b \phi(x) e^{-i \omega m x} dx &= \sum c_k \int_a^b e^{i \omega (k -m) x} dx \\ &= c_m (b - a) + \sum_{k \ne m} \frac{e^{i \omega(k-m) b} - e^{i \omega(k-m)a}}{i \omega (k -m)}. \end{aligned}


and switched it to dseries/dmath* in a way that I thought ought to have been allowed:

\begin{dseries}\label{eqn:fourierSeries:30a}
\begin{dmath*}
\int_a^b \phi(x) e^{-i \omega m x} dx
= \sum c_k \int_a^b e^{i \omega (k -m) x} dx
= c_m (b - a) + \sum_{k \ne m} \frac{e^{i \omega(k-m) b} - e^{i \omega(k-m)a}}{i \omega (k -m)}
\end{dmath*}
\end{dseries}


but get the error:

Package breqn Error: eq@repack penalty neq 0,1,2,3.


if I do this. It turns out that I can just use dmath like so as a work around:

\begin{dmath}\label{eqn:fourierSeries:30b}
\int_a^b \phi(x) e^{-i \omega m x} dx
= \sum c_k \int_a^b e^{i \omega (k -m) x} dx
= c_m (b - a) + \sum_{k \ne m} \frac{e^{i \omega(k-m) b} - e^{i \omega(k-m)a}}{i \omega (k -m)}
\end{dmath}


That numbers the set of equalities as one equation so that actually does exactly what I want. However, from the documentation, it doesn't look like what I did should be illegal. For example, the following (more subequation like form) also doesn't compile:

\begin{dseries}\label{eqn:fourierSeries:30c}
\begin{dmath*}
a = b + c
\end{dmath*}
\begin{dmath*}
a = b + c
\end{dmath*}
\end{dseries}


Here's a complete latex doc that demonstrates the error:

\documentclass[12pt]{scrreprt}
\usepackage{amsmath}
\usepackage{breqn}

\begin{document}

% original manually split:
%
%\label{eqn:fourierSeries:30} %\begin{aligned} %\int_a^b \phi(x) e^{-i \omega m x} dx %&= \sum c_k \int_a^b e^{i \omega (k -m) x} dx \\ %&= c_m (b - a) + \sum_{k \ne m} \frac{e^{i \omega(k-m) b} - e^{i \omega(k-m)a}}{i \omega (k -m)}. %\end{aligned} %

% works
%    \begin{dmath}\label{eqn:fourierSeries:30b}
%    \int_a^b \phi(x) e^{-i \omega m x} dx
%    = \sum c_k \int_a^b e^{i \omega (k -m) x} dx
%    = c_m (b - a) + \sum_{k \ne m} \frac{e^{i \omega(k-m) b} - e^{i \omega(k-m)a}}{i \omega (k -m)}
%    \end{dmath}

% both of these appear to break breqn
\begin{dseries}\label{eqn:fourierSeries:30a}
\begin{dmath*}
\int_a^b \phi(x) e^{-i \omega m x} dx
= \sum c_k \int_a^b e^{i \omega (k -m) x} dx
= c_m (b - a) + \sum_{k \ne m} \frac{e^{i \omega(k-m) b} - e^{i \omega(k-m)a}}{i \omega (k -m)}
\end{dmath*}
\end{dseries}

\begin{dseries}\label{eqn:fourierSeries:30a}
\begin{dmath*}
a = b + c
\end{dmath*}
\begin{dmath*}
a = b + c
\end{dmath*}
\end{dseries}

\end{document}


Do I misunderstand the point of the breqn dseries environment, or does it just not work?

• not sure immediately why it breaks (I get ! Dimension too large. on your MWE) but dseries doesn't seem to be the environment you want here it starts in text mode and is for making a sequence of in-line equations separated by text. seems like you'd just want dmath or to group them, dgroup – David Carlisle May 23 '12 at 15:52
• perhaps the error is version dependent. I've got: Package: breqn 2012/05/10 v0.98b Breaking equations <If you convert your comment to an answer, I could accept it.> – Peeter Joot May 24 '12 at 13:29

As suggested, posting this as a sort of non-answer. May try to trace later (the error difference at least)

not sure immediately why it breaks (I get ! Dimension too large. on your MWE) but dseries doesn't seem to be the environment you want here it starts in text mode and is for making a sequence of in-line equations separated by text. seems like you'd just want dmath or to group them, dgroup I used an older version but I'll update later and comment of it makes any real difference Package: breqn 2009/08/07 v0.98a Breaking equations