# Discretionary page break in an “align” display

Praesent quis nunc luctus, imperdiet leo in, rutrum nulla. Etiam vitae turpis sed risus rutrum luctus. Phasellus venenatis id erat ut consequat. Curabitur lacinia enim ac ipsum accumsan tempus.

\begin{align*}
f_Y(w) = {} & \frac 1 {\Gamma(\alpha_1)\Gamma(\alpha_2)} \int_0^\infty (wv)^{\alpha_1-1} e^{-wv} v^{\alpha_2} e^{-v} \, dv \\[6pt]
= {} & \frac 1 {\Gamma(\alpha_1)\Gamma(\alpha_2)} \cdot w^{\alpha_1-1} \int_0^\infty v^{\alpha_1+\alpha_2-1} e^{-(w+1)v} \,dv \\[6pt]
= {} &  \frac 1 {\Gamma(\alpha_1)\Gamma(\alpha_2)} \cdot \frac{w^{\alpha_1-1}}{(1+w)^{\alpha_1+\alpha_2}} \int_0^\infty ((w+1)v)^{\alpha_1+\alpha_2-1} e^{-(w+1)v} ((w+1)\,dv) \\[6pt]
= {} & \frac 1 {\Gamma(\alpha_1)\Gamma(\alpha_2)} \cdot \frac{w^{\alpha_1-1}{(1+w)^{\alpha_1+\alpha_2}} \int_0^\infty v^{\alpha_1+\alpha_2-1} e^{-v} \,dv \\[6pt]
= {} &  \frac {\Gamma(\alpha_1+\alpha_2)}{\Gamma(\alpha_1)\Gamma(\alpha_2)} \cdot \frac{w^{\alpha_1-1}}{(1+w)^{\alpha_1+\alpha_2}}
\end{align*}

Since there's not enough room on the page below "accumsan tempus" for this whole "align" display, LaTeX puts a page break there. But there is enough room for the first two lines of the display. Is there a standard way to get LaTeX to put the page break at whatever place within the display it finds to be necessary?

• Possible duplicate: Aligning equal signs in long equations – Werner Dec 12 '19 at 19:46
• The suggestion is to use \allowdisplaybreaks (see the amsmath documentation). – Werner Dec 12 '19 at 19:50
• @Werner : What if I want LaTeX to insert on the last line something like "continued on the next page$\,\longrightarrow$" at the appropriate spot? Is there a standard way to do that? – Michael Hardy Dec 12 '19 at 20:24
• It's better to leave such decisions at the last moment and place \displaybreak at the appropriate spot when no other solution is feasible; using \allowdisplaybreaks may end up in breaks at undesirable places. – egreg Dec 12 '19 at 20:45
• From the amsmath users guide: "When display breaks are enabled with \allowdisplaybreaks, the \\* command can be used to prohibit a pagebreak after a given line, as usual." – barbara beeton Dec 13 '19 at 3:06