# Custom pagebreak in align equation

I got the following problem: Right now I am checking my equations, which are usually written in align. This looks great in most of the cases, but sometimes the pagebreaks are weird, ie there is a lot of vertical whitespace left (like 2.5cm) at the end of a page. I made the following MWE to illustrate this.

\documentclass[a4paper, 12pt, headsepline]{scrreprt}
\usepackage[onehalfspacing]{setspace}
\usepackage{amsmath, amssymb, mathtools}
\usepackage{mathptmx}
\usepackage[a4paper]{geometry}
\geometry{left=2cm,right=5cm,top=2cm,bottom=2cm}
% \usepackage{lipsum} %\lipsum
\usepackage[pangram]{blindtext}

\begin{document}
\Blindtext[1][3]%1 paragraph, 3 pangrams
\begin{align}
X_{t+1} &=  \frac{X_{t+1}+X_{t+1}}{Y_t}  \label{eq:1}
\intertext{Solving...:} \notag
X_{t}  &=  \frac{X_{t+1}+X_{t+1}}{Y_{t+1}} \notag \\
\intertext{Solving further...:} \notag
% ===PAGEBREAK HERE: 2nd page begins===
&= \frac{X_{t+1}+X_{t+1}}{Y_t} +
\frac{X_{t+1}+X_{t+1}}{Y_t}  \notag \\
&= \frac{X_{t+1}+X_{t+1}}{Y_t}...  \notag \\
\intertext{Solving further...:} & = \frac{X_{t+1}+X_{t+1}}{Y_t}  \notag
\end{align}
\end{document}


In the MWE, the first 'Solving further' should be on the first page instead (to save space and it would also look better I guess?). The position where I would like the pagebreak to be is also marked as a comment in the MWE.

My question is first on a general basis: Which is the best environment to achieve multiple line equations, which can be aligned as in align, and to save space at the same time? Or to be more precise: If possible, I'd like to stick with align and adapt the pagebreaks only if necessary.

Thanks!

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but, from p.189 of the texbook: "Plain TeX sets \predisplaypenalty=100000, because fine printers traditionally shun displayed formulas at the very top of a page." you might consider using \shortintertext (defined in mathtools) to save space when the text really doesn't overlap the displayed material. – barbara beeton Dec 23 '13 at 20:02
@barbarabeeton Ok so you recommend not to follow the below solution, but instead to use shortintertext cmds? – TomM Dec 23 '13 at 20:11
it's your paper, so it's really your choice. but you might try \shortintertext to see if it's an improvement. it might set the lines closer together than you want, because you're using onehalfspacing, but math displays always get extra space anyhow. the only way to find out is to try it in your particular context. – barbara beeton Dec 23 '13 at 20:16
@barbarabeeton alright thanks for the explanation. – TomM Dec 23 '13 at 20:39

If you want automatic page breaks you have to use the command \allowdisplaybreaks in your preamble.

If you want manual page breaks, you have to use the command \displaybreak followed by \\, as in the following MWE:

\documentclass[a4paper, 12pt, headsepline]{scrreprt}
\usepackage[onehalfspacing]{setspace}
\usepackage{amsmath, amssymb, mathtools}
\usepackage{mathptmx}
\usepackage[a4paper]{geometry}
\geometry{left=2cm,right=5cm,top=2cm,bottom=2cm}
% \usepackage{lipsum} %\lipsum
\usepackage[pangram]{blindtext}

\begin{document}
\Blindtext[1][3]%5 paragraphs, each 3 pangrams
\begin{align}
X_{t+1} &=  \frac{X_{t+1}+X_{t+1}}{Y_t}  \label{eq:1}
\intertext{Solving...:} \notag
X_{t}  &=  \frac{X_{t+1}+X_{t+1}}{Y_{t+1}} \notag \\
\intertext{Solving further...:} \notag \displaybreak\\
% ===PAGEBREAK HERE: 2nd page begins===
&= \frac{X_{t+1}+X_{t+1}}{Y_t} +
\frac{X_{t+1}+X_{t+1}}{Y_t}  \notag \\
&= \frac{X_{t+1}+X_{t+1}}{Y_t}...  \notag \\
\intertext{Solving further...:} & = \frac{X_{t+1}+X_{t+1}}{Y_t}  \notag
\end{align}
\end{document}


Output

-
thanks for the quick reply! – TomM Dec 23 '13 at 20:00

use

[...]
\allowdisplaybreaks%%%%%
\begin{document}
\Blindtext[1][3]%5 paragraphs, each 3 pangrams
\begin{align}
X_{t+1} &=  \frac{X_{t+1}+X_{t+1}}{Y_t}  \label{eq:1}
\intertext{Solving...:} \notag
X_{t}  &=  \frac{X_{t+1}+X_{t+1}}{Y_{t+1}} \notag \\
\intertext{Solving further...:}
&= \frac{X_{t+1}+X_{t+1}}{Y_t} + \frac{X_{t+1}+X_{t+1}}{Y_t}  \notag \\
&= \frac{X_{t+1}+X_{t+1}}{Y_t}...  \notag \\
\intertext{Solving further...:} & = \frac{X_{t+1}+X_{t+1}}{Y_t}  \notag
\end{align}
\end{document}


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thanks for your answer. I'd accepted both if possible because both are correct. To be fair I accepted the faster entry. – TomM Dec 23 '13 at 19:59