# Breaking an array of equations

I wanted to break long equations in an array environment. To do this, I used dmath environment from breqn package but it did not work. How can I write long equations in an array environment with line breaks? My attempt is as follows:

\documentclass[11pt,twocolumn]{article}
\usepackage{amsmath}
\usepackage{breqn}
\begin{document}
\begin{dmath*}
L_{\lambda}(\phi, \omega) =
\left\lbrace
\begin{array}{ll}
a \times b \times c \times d \times e \times f \times g \times h \times i \times j \times k \times l \condition[]{for $\phi$ even},
\\
a \times b \times c \times d \times e \times f \times g \times h \times i \times j \times k \times l \condition[]{for $\phi$ odd},
\end{array}
\right.
\end{dmath*}
\end{document}


# EDIT: Actual Equation :

I thought the solution will be general so posted a nicer version of the problem earlier. Following is the actual equation I want to typeset. How can I typeset this equation nicely even with manual line breaks?

\begin{dmath*}
L_{\lambda}(\phi, \omega) =
\left\lbrace
\begin{array}{ll}
2 \cos
\left[
\tanh \left(
\frac{L_{\lambda-1}(\psi, \omega)}{2}
\right) \times \tanh \left(
\frac{L_{\lambda-1}(\psi, \omega+1)}{2}
\right)
\right] \condition[]{for $\phi$ even},
\\
2 \sin
\left[
\tanh \left(
\frac{B_{\lambda-1}(\psi, \omega+1)}{2}
\right) \times \tanh \left(
\frac{L_{\lambda-1}(\psi, \omega)}{2}
\right)
\right] \condition[]{for $\phi$ odd},
\end{array}
\right.
\end{dmath*}

-
an array l column is always one line. You need (or could) use instead p columns of fixed width containing inline math $a \times b ....$ the inline math would wrap to the specified column width in standard latex even without breqn. – David Carlisle Jul 20 '12 at 16:29

As David Carlisle has already pointed out in a comment, you can't have a line break inside an array environment (at least not in a column of type l). The only possible break point in the equation you describe is right after the L_{\lambda}(\phi, \omega) part.

If the equation you've posted is really what you need to typeset -- I somehow doubt it, but that is what you've posted... -- your best bet may be to (i) replace all \times symbols with \cdot symbols and (ii) reduce the font size by 1 pt (by issuing the instruction \small) for the equation in question. (Note that I've also gotten rid of the array stuff in favor of a cases* environment.)

\documentclass[11pt,twocolumn]{article}
\usepackage{mathtools,breqn}
\usepackage{mathtools,breqn}
\def\filler{Nam dui ligula, fringilla a, euismod sodales,
sollicitudin vel, wisi. Morbi auctor lorem non justo.
Nam lacus libero, pretium at, lobortis vitae, ultricies
et, tellus.}
\begin{document}
{\small
\begin{dmath*}
L_{\lambda}(\phi, \omega) =
\begin{cases*}
a\cdot b\cdot c\cdot d\cdot e\cdot f\cdot g\cdot h\cdot i\cdot j\cdot
k\cdot l & for $\phi$ even, \\
a\cdot b\cdot c\cdot d\cdot e\cdot f\cdot g\cdot h\cdot i\cdot j\cdot
k\cdot l & for $\phi$ odd.
\end{cases*}
\end{dmath*}
} % end of scope of \small statement
\filler % filler text, to show width of text column
\end{document}


However, it would seem to be the case that you would rather have the line break (or breaks) occur somewhere to the right of the big curly brace. Here's a suggested solution which uses the split environment:

\documentclass[11pt,twocolumn]{article}
\usepackage{mathtools}
\def\filler{Nam dui ligula, fringilla a, euismod sodales,
sollicitudin vel, wisi. Morbi auctor lorem non justo.
Nam lacus libero, pretium at, lobortis vitae, ultricies
et, tellus.}

\begin{document}
\begin{equation*}
L_{\lambda}(\phi, \omega) =
\begin{dcases}
\begin{split}
a\cdot b\cdot c\cdot d\cdot e\cdot f\cdot g \\
{}\cdot h\cdot i\cdot j\cdot k\cdot l
\end{split}
& \text{for $\phi$ even,} \\
\begin{split}
a\cdot b\cdot c\cdot d\cdot e\cdot f\cdot g \\
{}\cdot h\cdot i\cdot j\cdot k\cdot l
\end{split}
& \text{for $\phi$ odd.}
\end{dcases}
\end{equation*}

\noindent\filler
\end{document}


Addendum: I just noticed that you posted the actual math expression you're trying to typeset. Here's how I would try to get the job done: building on the two previous examples, I'd allow a line break both after L_{\lambda}(\phi, \omega) -- fully automatic, courtesy of breqn and the dmath* environment -- and within each of the longish expressions to the right of the large curly brace.

\documentclass[11pt,twocolumn]{article}
\usepackage{mathtools,breqn}
\def\filler{Nam dui ligula, fringilla a, euismod sodales,
sollicitudin vel, wisi. Morbi auctor lorem non justo.
Nam lacus libero, pretium at, lobortis vitae, ultricies
et, tellus.}
\begin{document}
\begin{dmath*}
L_{\lambda}(\phi, \omega) =
\begin{dcases}
\begin{split}
2 \cos \Bigg[ \tanh \left(\frac{L_{\lambda-1}
(\psi, \omega)}{2}\right) \ \ \ \ \ \\
% need to "shove" the first line to the left
\times \tanh \left(\frac{L_{\lambda-1}
(\psi, \omega+1)}{2}\right) \Bigg]
\end{split}
& \text{for $\phi$ even,}\\
\begin{split}
2 \sin\Bigg[ \tanh \left( \frac{B_{\lambda-1}
(\psi, \omega+1)}{2} \right) \\
\times \tanh \left( \frac{L_{\lambda-1}
(\psi, \omega)}{2} \right) \Bigg]
\end{split}
& \text{for $\phi$ odd.}
\end{dcases}
\end{dmath*}
\filler %% filler text, to show width of text block
\end{document}


-
This is not the equation I wanted to typeset but the problem is similar. So, I changed the messy equation with a nicer one. I thought there would be a general solution. Can we manually break lines with alignment similar to breqn? – ubaabd Jul 20 '12 at 16:48
@ubaabd: You can always insert a manual break. However, you need to be more clear in your question as to what exactly you're after in terms of that. – Werner Jul 20 '12 at 16:56
@ubaad: I've posted an addendum to show how one can use the split environment to force line breaks. – Mico Jul 20 '12 at 17:12
@Werner I posted the actual equation. How do you think should I manually line break this equation or what is the general trend that people follow with these kind of equations, as I suspect from your answers, there is no automatic way of doing this in Latex. – ubaabd Jul 20 '12 at 17:14
@mico Thanks Mico! Thats exactly what I wanted, i.e., proper alignment even after line breaks. – ubaabd Jul 20 '12 at 17:15