@Section
   @Title { Optimal galley breaking }
   @Tag { optimal }
@Begin
@PP
As explained in Section {@NumberOf targets}, the components of a galley
optimal.gall @Index { Optimal galley breaking }
are promoted one by one into a target.  When space runs out there, the
galley searches for a new target and promotion resumes.
@PP
This process is exactly analogous to placing words onto a line until
space runs out, then moving to another line.  But, as we know, that
simple method is inferior to the optimal paragraph breaking used by
Lout (copied from the @TeX system), which examines the entire paragraph
and determines the most even assignment of words to lines.
@PP
Lout offers @I { optimal galley breaking }, the equivalent for galleys
of optimal paragraph breaking.  Optimal galley breaking can reduce the
size of ugly blank spaces at the bottom of pages preceding large
unbreakable displays, sometimes quite dramatically.
@PP
Optimal galley breaking is applied to each galley, horizontal or
vertical, that possesses a parameter or nested symbol called
@Code "@Optimize" whose value is {@Code Yes}.  Like cross referencing,
optimize.sym @Index { @Code "@Optimize" symbol }
it takes two runs to have effect.  On the first run, Lout records the
sizes of the galley's components and gaps, and also the space available
at each of its targets.  At end of run this information is used to find
an optimal break, which is written to the cross-reference database.  On
the second run, the optimal break is retrieved and used.
@PP
Considering that this process must cope with floating figures,
new page and conditional new page symbols, breaks for new chapters, and
evolving documents, it is surprisingly robust.  If it does go badly
wrong, removing file @Code "lout.li" then running Lout twice without
changing the document may solve the problem.  However, cases are known
where the optimization never converges.  These are usually related to
figures and footnotes whose anchor points fall near page boundaries.
@End @Section