%% LTabPtch.sty---Uwe L"uck---patch for Longtable. 
\def\filedate{2005/01/10} \def\fileversion{1.74d}
%% For David Carlisle's Longtable.sty, version 4.11 
%% Fixes tools/3180 (Sebastian Rahtz) and tools/3485: 
%% missing/wrong interline glues above/below table. 
%% 
%% Copyright (C) 2002--2004 Uwe L"uck, 
%% http://www.contact-ednotes.sty.de.vu 
%% --author-maintained. 
%%
%% Usage, no warranty, distribution as in lppl.txt on CTAN 
%% (macros/latex/base/lppl.txt). 
%% 
%% Loading Longtable.sty with options must be done earlier! 
%% 
\NeedsTeXFormat{LaTeX2e}[1994/05/20] % \CheckCommand 
\ProvidesPackage{ltabptch}[\filedate\space v\fileversion\space
   Longtable patch for tools/3180, 3485 (ul)]
% 
% The problem(s): 
% Sebastian Rahtz (tools/3180) observed 2000/03/05 that there be 
% a "spurios blank line" below the longtable. This impression 
% may have been due to two spacing problems: 
% (1) There is \parskip and some interline glue below longtable, 
% while there is no \parskip and no interline glue above 
% (without head as specified by \endhead or \firstendhead) 
% or just \lineskip 0.0pt (with head---\endhead, \endfirsthead). 
% (2) After longtable, \prevdepth is the depth of the last line 
% before the longtable (if there is no head) or the depth of the 
% head (otherwise). So \prevdepth may be 0pt. By contrast, the 
% last table row has depth of at least \dp\@arstrutbox--which 
% should rather matter, and this is 3.6pt or more. 
% --I have reported something like this as tools/3485, not 
% entirely correctly. Details are presented below \endinput. 
% 
% Solution presented: 
% (1) I think there should be \parskip and usual interline glue 
% above, since the same would happen with a table in a center 
% environment (e.g.). 
% \noindent seems to work fatally; moreover, \LT@start's decision 
% whether to enter a new page would ignore \parskip and interline 
% glue still needed. 
% So emulate interline glue calculation according to TeXbook p. 80 
% and add it by \vskip, along with \parskip. 
% (This is rather a hack---a proper correction should perhaps not 
% "emulate" but place the interlineglue changes of \LT@array inside 
% the \vbox \LT@bchunk starts and treat glue between chunks in a 
% new way.) 
% (2) Set \prevdepth to depth of box 0 before the latter is 
% \unvbox'ed (which leaves \prevdepth untouched, TeXbook p. 282) 
% in \endlongtable. 
% 
% I thought David Carlisle would change Longtable according to my 
% suggestions. By e-mail from 2003/04/07 however, he finds it 
% better not to change Longtable, in order not to change layouts 
% of works that have been made using Longtable so far 
% (e-Mail 2003/04/08). 
% 
%% <- TODO: change this when David has changed his mind! 
% By the way: 
% 1.) There are two successive lines in the Longtable code (v4.11) 
%     together saying: 
%         \prevdepth\z@\global 
%         \global\let\LT@setprevdepth\relax 
%     Isn't the first \global just a typo? 
%     --Yes--this is David Carlisle's answer in his e-mail 
%     dating from 2004/05/14. 
% 2.) Couldn't the one-column restriction easily be removed 
%     by using \columnwidth instead of \hsize? 
% 
% Patching is to override Longtable.sty: 
\RequirePackage{longtable}[2004/02/01] 
%% TODO: Cf. \CheckCommand below. 
% Load earlier on your own for choosing Longtable options! 
% 
% For (1), we are patching \LT@start, assumed to have been defined 
% as follows (Longtable v4.11; sorry we can no longer handle v3.16 
% through 4.10): 

\CheckCommand*{\LT@start}{%
  \let\LT@start\endgraf
  \endgraf\penalty\z@\vskip\LTpre
  \dimen@\pagetotal
  \advance\dimen@ \ht\ifvoid\LT@firsthead\LT@head\else\LT@firsthead\fi
  \advance\dimen@ \dp\ifvoid\LT@firsthead\LT@head\else\LT@firsthead\fi
  \advance\dimen@ \ht\LT@foot
  \dimen@ii\vfuzz
  \vfuzz\maxdimen
    \setbox\tw@\copy\z@
    \setbox\tw@\vsplit\tw@ to \ht\@arstrutbox
    \setbox\tw@\vbox{\unvbox\tw@}%
  \vfuzz\dimen@ii
  \advance\dimen@ \ht
        \ifdim\ht\@arstrutbox>\ht\tw@\@arstrutbox\else\tw@\fi
  \advance\dimen@\dp
        \ifdim\dp\@arstrutbox>\dp\tw@\@arstrutbox\else\tw@\fi
  \advance\dimen@ -\pagegoal
  \ifdim \dimen@>\z@\vfil\break\fi
      \global\@colroom\@colht
  \ifvoid\LT@foot\else
    \advance\vsize-\ht\LT@foot
    \global\advance\@colroom-\ht\LT@foot
    \dimen@\pagegoal\advance\dimen@-\ht\LT@foot\pagegoal\dimen@
    \maxdepth\z@
  \fi
  \ifvoid\LT@firsthead\copy\LT@head\else\box\LT@firsthead\fi\nobreak 
%% \nobreak new with Longtable v4.11. 
  \output{\LT@output}}
% 
% Change it: 
\def\LT@start{%
  \let\LT@start\endgraf
  \endgraf\penalty\z@\vskip\LTpre
 \vskip\parskip %% U.L. 
% I want to add the interline glue before \pagetotal goes to \dimen@. 
% So I move \LT@start's \vsplit here. 
 %% U.L. start: 
 \dimen@ii\vfuzz 
 \vfuzz\maxdimen
   \setbox\tw@\copy\z@
   \setbox\tw@\vsplit\tw@ to \ht\@arstrutbox
   \setbox\tw@\vbox{\unvbox\tw@}%
 \vfuzz\dimen@ii
 \ifdim\prevdepth>-\@m\p@ 
% First we need the maximum of the heights of \tw@ and head row. 
% A little flaw might be here: I am ignoring \Lt@start's 
% \@arstrutbox concern below, cf. remark there. 
   \@tempskipa % \normalbaselineskip going to enter. 
     \ht\ifvoid\LT@firsthead\LT@head\else\LT@firsthead\fi 
%  \typeout{\@tempskipa=\the\@tempskipa}% TEST 
   \@tempskipa-\ifdim\@tempskipa<\ht\tw@\ht\tw@\else\@tempskipa\fi 
%  \typeout{\@tempskipa=\the\@tempskipa}% TEST 
   \advance\@tempskipa-\prevdepth 
%  \typeout{\string\prevdepth=\prevdepth}% TEST 
%  \typeout{\@tempskipa=\the\@tempskipa}% TEST 
   \advance\@tempskipa\normalbaselineskip 
%  \typeout{\normallineskiplimit=\the\normallineskiplimit}% TEST 
%  \typeout{\@tempskipa=\the\@tempskipa}% TEST 
   \vskip \ifdim\@tempskipa<\normallineskiplimit 
            \normallineskip 
          \else 
            \@tempskipa 
          \fi 
 \fi 
 \nointerlineskip % v1.4 prevent head from adding more 
%                 % (if only negative) glue. 
%  \prevdepth -1000\p@ % Prevent head from adding more glue (v1.3). 
 %% U.L. end. 
  \dimen@\pagetotal
  \advance\dimen@ \ht\ifvoid\LT@firsthead\LT@head\else\LT@firsthead\fi
  \advance\dimen@ \dp\ifvoid\LT@firsthead\LT@head\else\LT@firsthead\fi
  \advance\dimen@ \ht\LT@foot
%   \dimen@ii\vfuzz
%   \vfuzz\maxdimen
%     \setbox\tw@\copy\z@
%     \setbox\tw@\vsplit\tw@ to \ht\@arstrutbox
%     \setbox\tw@\vbox{\unvbox\tw@}%
%   \vfuzz\dimen@ii
% 
% Remark U.L.: The following four code lines seem strange to me: 
% after all, \tw@ contains \@arstrutbox, doesn't it? 
% And even if not: why should we need room for another \@arstrutbox? 
  \advance\dimen@ \ht
        \ifdim\ht\@arstrutbox>\ht\tw@\@arstrutbox\else\tw@\fi
  \advance\dimen@\dp
        \ifdim\dp\@arstrutbox>\dp\tw@\@arstrutbox\else\tw@\fi
  \advance\dimen@ -\pagegoal
  \ifdim \dimen@>\z@\vfil\break\fi
      \global\@colroom\@colht
  \ifvoid\LT@foot\else
    \advance\vsize-\ht\LT@foot
    \global\advance\@colroom-\ht\LT@foot
    \dimen@\pagegoal\advance\dimen@-\ht\LT@foot\pagegoal\dimen@
    \maxdepth\z@
  \fi
  \ifvoid\LT@firsthead\copy\LT@head\else\box\LT@firsthead\fi\nobreak 
%% \nobreak new with Longtable 4.11. 
  \output{\LT@output}}
% 
% 
% For (2), we are patching \endlongtable: 
% The patch should not change essentials of \endlongtable 
% which may have changed when this patch meets longtable. 
% We just assume that the final contribution to the main vertical 
% list is done by \unvbox0 which is preceded by \LT@start. 
% \prevdepth\dp0 can be put in between, it will then 
% last till the end (TeXbook pp. 282, 277f.). 
\def\@tempa#1\LT@start{#1\LT@start \prevdepth\dp\z@} 
\expandafter\expandafter\expandafter \def 
 \expandafter\expandafter\expandafter \endlongtable 
  \expandafter\expandafter\expandafter 
   {\expandafter\@tempa\endlongtable} 
% 
\endinput 

DETAILED DIAGNOSIS: 

Concerning the question of "bugs" vs. "features", you might 
reason what features should be aimed at. 

%% TODO: This can be shortened when David agrees. 

    (A) If there is \parskip below a longtable, there should 
be \parskip above as well--shouldn't it? 
    (B) Interline glue above should (in general) depend on the 
same values of \baselineskip and \lineskip as below---OK? 
    (C) Interline glue below a longtable should depend on the 
depth of the last row, not on the depth of the head or of the 
last line above the longtable--OK? 

The recent versions of longtable.sty have not satisfied any 
of these three demands. 
Concerning (A), \parskip appears below the longtable, but not 
above. 
Concerning (B), (i) no interline glue appears above if there 
is no head, (ii) otherwise, only zero interline glue appears.
Concerning (C), the interline glue below the longtable is 
calculated using the depth of (i) the last line above the 
longtable as \prevdepth when there is no head or of (ii) the 
head otherwise. (Thus I was wrong earlier when I claimed that 
\prevdepth were 0pt after longtable. This only holds in the 
previous case (i) when the last line above the longtable has 
zero depth.)

You can observe this by playing with the demonstration file 
ltabptch.tex in CTAN folder macros/latex/contrib/ltabptch. 

Reasons: For contributing a head to the main vertical list, 
longtable uses \copy or \box, which yields a <box> according 
to TeXbook p. 278. Rows are contributed by \unvbox. Now, 
violation of (A) is due to the fact that neither \copy or 
\box of the head nor the \unvbox for table rows leads to 
execution of an \indent or \noindent (TeXbook pp. 282f., see 
also <horizontal command>). 
Violation of (B) is due either to (i) the fact that \unvbox 
is no <box> (TeXbook p. 282/278) or to (ii) the fact that at 
\copy or \box \baselineskip and \lineskip are 0pt. 
Violation of (C) is due to the fact that \unvbox does not 
change \prevdepth (TeXbook p. 282). 

As to recognizable effects: 
    Violation of (A), of course, has very little effect in 
general since \parskip is 0pt plus 1pt usually. This is hardly 
recognizable in the presence of the \bigskipamount above and 
below a longtable. 
    Violation of (B) results in missing appropriate interline 
glue above, which often should be 3.6pt or more. This may 
rather be recognizable and may contribute to the impression 
that there even is a spurious blank line below the longtable 
(this is what Sebastion Rahtz reported in tools/3180). 
    For the previous as well as for the details and the 
effects of violation of (C), consider the algorithm for 
calculating interline glue on p. 80 of the TeXbook. If there 
is no head, and the depth of the last line before the 
longtable is 0pt, the interline glue below the longtable is 
\baselineskip minus the height of the first line after the 
longtable. The interline glue *should be* \baselineskip minus 
height of following line *minus* depth of last table row--if 
this depth is not too large (depending on \lineskiplimit). 
This depth is at least 3.6pt. So the interline glue is often 
by 3.6pt or more greater than is appropriate. Considering the 
missing interline glue above the longtable and the \parskip 
below, the glue after the longtable is by 6.2pt (or more) plus 
1pt larger than the glue before. Due to the shrink component 
of the surrounding \bigskipamount, the glue following the 
longtable may be nearly twice as large as the glue before.
---Usually, violation of (C) has no effect at all. Namely, 
there is a head usually, and its depth is usually the same as 
the depth of the last row, namely \dp\@arstrutbox. 


%% VERSION HISTORY: 
v1.7  2003/01/07 Sent around 2003/01/13 with first release of 
                 ednotes.sty. Sent to David Carlisle. Earlier versions 
                 were sent to Frank Mittelbach and the team. 
v1.71 2003/01/22 Added version history. 
v1.72 2003/01/27 Changed copyright notice. 
v1.73 2004/05/13 Adapted to Longtable v4.11; new copyright; 
                 longtable -> Longtable (selectively). 
                 Added `I have ... 3485'. 
v1.74 2004/08/05 Added `---Yes---...'. 
      2004/08/21 Typo fix for `problem'; added report on 2003/04/08. 
      2004/08/23 Corrected and extended diagnosis, sent to CTAN. 
v1.74b .../08/23 `---' -> `--'; added that (C) usually doesn't 
                 matter. 
v1.74c .../08/31 `author-maintained'. 
v1.74d 2005/01/10 Contact via http.