[luatex] Strange cost in pagebreaking.

[luigi scarso]

On Tue, Oct 15, 2013 at 10:08 PM, Paul Isambert <zappathustra at free.fr>wrote:

> Hello all,
>
> I’ve encountered a problem which I definitely can’t solve. It looks
> like a TeX problem, but since I really can’t see what’s going on I
> suspect a LuaTeX bug. Unfortunately the problem is extremely sensitive
> to simple changes, and so I can’t even compare with a PDFTeX
> compilation. (And since there is a lot of my own code involved, I
> cannot do a minimal example either.)
>
> Here’s what \tracingpages returns in my log file (until the current
> page is deemed good):
>
> 1.  %% goal height=569.05511, max depth=4.0
> 2.  % split251 to 0.0,38.12 p=-10000
> 3.  % split252 to 0.0,103.05 p=-10000
> 4.  % t=0.0 g=498.47559 b=10000 p=0 c=100000#
> 5.  % t=22.0 g=498.47559 b=10000 p=150 c=100000#
> 6.  % t=45.22 g=498.47559 b=10000 p=0 c=100000#
> 7.  % t=70.16 g=498.47559 b=10000 p=0 c=100000#
> 8.  % t=93.27 g=498.47559 b=10000 p=150 c=100000#
> 9.  % t=105.27 g=498.47559 b=10000 p=0 c=100000#
> 10. % t=121.27 plus 1.0fil g=498.47559 b=0 p=150 c=-19850#
> 11. % t=133.27 plus 1.0fil g=498.47559 b=0 p=0 c=-20000#
> 12. % t=145.27 plus 1.0fil g=498.47559 b=0 p=0 c=-20000#
> 13. % t=157.27 plus 1.0fil g=498.47559 b=0 p=150 c=-19850
> 14. % t=169.27 plus 1.0fil g=498.47559 b=0 p=0 c=-20000#
> 15. % t=185.27 plus 2.0fil g=498.47559 b=0 p=150 c=-19850
> 16. % t=197.27 plus 2.0fil g=498.47559 b=0 p=150 c=-19850
> 17. % t=209.27 plus 2.0fil g=498.47559 b=0 p=0 c=-20000#
> 18. % t=209.27 plus 3.0fil g=498.47559 b=0 p=-11000 c=-11000
>
> What bothers me is line 10 and following: where does the cost of
> -20000 comes from? There is no penalty of that value for each of those
> line, so I really can’t see how it can be computed (since, basically,
> the cost of a breakpoint is badness + penalty). Then the page is
> broken at the wrong place – even though breaking is of course
> triggered by the big negative penalty at line 18.
>
> (You may note that outputting the page at line 17 instead of 18
> doesn’t change anything, since no material is added, so this
> troublesome bahavior isn’t so troublesome; well, actually it is, when
> you’re expecting a given \outputpenalty.)
>
> So, have I missed some obvious subtlety?
>
> Best,
> Paul
>
> Maybe in buildpage there is something more:

$> cweave buildpage.w
$> pdftex buildpage.tex

buildpage.w  is into
source/texk/web2c/luatexdir/tex

-- 
luigi
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