What is the vertical spacing caused by the \intertext or \shortintertext command?

Question

\documentclass[letterpaper,10pt]{article}
\usepackage{amsmath}
\usepackage{nccmath}

\begin{document}

\begin{align*}
\intertext{what is the vertical spacing here?} \\[-30pt] 1+2 \\
=3
\end{align*}
\end{document}

There is an automatic vertical gap that the \intertext command inserts. I would like to know how many pts that gap is to exactly get rid of it with the \\[...] command explicit since manually adjusting this height gives me the freedom I require. -30pts is close, but it appears no integer value works and the ams manual doesn't specify the exact spacing of the intertext command.

Related: Vertical space command which is between \intertext and \shortintertext — Werner, Jan 06 '19 at 07:05
Possibly related: How can I add left aligned text to an equation? — Werner, Jan 06 '19 at 07:05
use of \intertext here is simply user error, using negative spacing will in general cause it to over-print the equation. It is not that \intertext adds vertical space, it is that it adds a line of text after the equation. If you want to add text within the equation then you should use \text or similar commands. — David Carlisle, Jan 06 '19 at 10:31
It's not technically align* since it uses flalign*, but I will give it a try tomorrow and see if it works, doesn't seem like a large change. — user14554, Jan 06 '19 at 10:32
The duplication suggestion here seemed reasonable to me on the basis of this being an 'XY question': asking about a technical aspect with the ultimate aim being to address a wider layout issue. However, as you are clear that you really do require only detail of the technical aspect, I've reopened. I suggest you edit the question to make the focus absolutely explicit. — Joseph Wright, Jan 08 '19 at 08:59

score 5 · Accepted Answer · answered Jan 06 '19 at 07:02

If you add \showoutput to your code, you can see the vertical spaces added by TeX to construct the output page. So,

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\showoutput
\begin{align*}
  top \\
  \intertext{intertext}
  bottom
\end{align*}

\end{document}

yields in your .log:

Completed box being shipped out [1]
\vbox(633.0+0.0)x407.0
.\hbox(0.0+0.0)x0.0
..\kern -72.26999
..\vbox(0.0+0.0)x345.0, glue set 72.26999fil
...\kern -72.26999
...\glue(\parskip) 0.0
...\hbox(0.0+0.0)x345.0, glue set 345.0fil
....\hbox(0.0+0.0)x0.0
....\hbox(0.0+0.0)x0.0
.....\hbox(0.0+0.0)x0.0
......\glue 0.0
......\hbox(0.0+794.96999)x0.0
.......\hbox(0.0+0.0)x0.0, shifted 794.96999
........\kern 0.0
........\glue 0.0 plus 1.0fil minus 1.0fil
......\glue 0.0 plus 1.0fil minus 1.0fil
....\penalty 10000
....\glue(\parfillskip) 0.0 plus 1.0fil
....\glue(\rightskip) 0.0
...\glue 0.0 plus 1.0fil minus 1.0fil
.\glue 16.0
.\vbox(617.0+0.0)x345.0, shifted 62.0
..\vbox(12.0+0.0)x345.0, glue set 12.0fil
...\glue 0.0 plus 1.0fil
...\hbox(0.0+0.0)x345.0
....\pdfcolorstack 0 push {0 g 0 G}
....\hbox(0.0+0.0)x345.0
....\pdfcolorstack 0 pop
..\glue 25.0
..\glue(\lineskip) 0.0
..\vbox(550.0+0.0)x345.0, glue set 457.95108fil
...\write-{}
...\pdfcolorstack 0 push {0 g 0 G}
...\glue(\topskip) 10.0
...\hbox(0.0+0.0)x345.0, glue set 330.0fil
....\hbox(0.0+0.0)x15.0
....\penalty 10000
....\glue(\parfillskip) 0.0 plus 1.0fil
....\glue(\rightskip) 0.0
...\penalty 10000
...\glue(\abovedisplayskip) 10.0 plus 2.0 minus 5.0
...\glue -3.0
...\glue 0.0
...\glue(\baselineskip) 6.60004
...\hbox(8.39996+3.60004)x187.49423, display
....\glue(\tabskip) 157.50575
....\hbox(8.39996+3.60004)x29.98848, glue set 16.49889fil
.....\glue 0.0 plus 1.0fil
.....\hbox(8.39996+3.60004)x0.0
......\vbox(8.39996+3.60004)x0.0
.......\kern 0.0
.......\hbox(8.39996+3.60004)x0.0
........\rule(8.39996+3.60004)x0.0
.....\hbox(6.15079+1.94444)x13.4896
......\mathon
......\hbox(6.15079+1.94444)x13.4896
.......\OML/cmm/m/it/10 t
.......\OML/cmm/m/it/10 o
.......\OML/cmm/m/it/10 p
......\mathoff
....\glue(\tabskip) 0.0
....\hbox(8.39996+3.60004)x0.0
.....\hbox(0.0+0.0)x0.0
......\mathon
......\hbox(0.0+0.0)x0.0
......\mathoff
.....\glue 0.0 plus 1.0fil
....\glue(\tabskip) 157.50575
....\hbox(8.39996+3.60004)x-157.50575
.....\kern -157.50575
....\glue(\tabskip) 0.0
...\penalty 10000
...\glue 0.0
...\penalty 0
...\glue 10.0 plus 2.0 minus 5.0
...\glue(\baselineskip) 4.72137
...\vbox(6.67859+0.0)x345.0
....\hbox(6.67859+0.0)x345.0, glue set 307.19437fil
.....\OT1/cmr/m/n/10 i
.....\OT1/cmr/m/n/10 n
.....\kern-0.27779
.....\OT1/cmr/m/n/10 t
.....\OT1/cmr/m/n/10 e
.....\OT1/cmr/m/n/10 r
.....\OT1/cmr/m/n/10 t
.....\OT1/cmr/m/n/10 e
.....\OT1/cmr/m/n/10 x
.....\OT1/cmr/m/n/10 t
.....\penalty 10000
.....\glue(\parfillskip) 0.0 plus 1.0fil
.....\glue(\rightskip) 0.0
...\penalty 10000
...\glue 10.0 plus 2.0 minus 5.0
...\glue(\baselineskip) 6.60004
...\hbox(8.39996+3.60004)x187.49423, display
....\glue(\tabskip) 157.50575
....\hbox(8.39996+3.60004)x29.98848
.....\glue 0.0 plus 1.0fil
.....\hbox(8.39996+3.60004)x0.0
......\vbox(8.39996+3.60004)x0.0
.......\kern 0.0
.......\hbox(8.39996+3.60004)x0.0
........\rule(8.39996+3.60004)x0.0
.....\hbox(6.94444+0.0)x29.98848
......\mathon
......\hbox(6.94444+0.0)x29.98848
.......\OML/cmm/m/it/10 b
.......\OML/cmm/m/it/10 o
.......\OML/cmm/m/it/10 t
.......\OML/cmm/m/it/10 t
.......\OML/cmm/m/it/10 o
.......\OML/cmm/m/it/10 m
......\mathoff
....\glue(\tabskip) 0.0
....\hbox(8.39996+3.60004)x0.0
.....\hbox(0.0+0.0)x0.0
......\mathon
......\hbox(0.0+0.0)x0.0
......\mathoff
.....\glue 0.0 plus 1.0fil
....\glue(\tabskip) 157.50575
....\hbox(8.39996+3.60004)x-157.50575
.....\kern -157.50575
....\glue(\tabskip) 0.0
...\penalty 10000
...\glue 0.0
...\penalty 0
...\glue(\belowdisplayskip) 10.0 plus 2.0 minus 5.0
...\glue -3.60004
...\glue 0.0 plus 1.0fil
...\glue 0.0
...\glue 0.0 plus 0.0001fil
..\glue(\baselineskip) 23.55556
..\hbox(6.44444+0.0)x345.0
...\pdfcolorstack 0 push {0 g 0 G}
...\hbox(6.44444+0.0)x345.0, glue set 170.0fil
....\glue 0.0 plus 1.0fil
....\OT1/cmr/m/n/10 1
....\glue 0.0 plus 1.0fil
...\pdfcolorstack 0 pop
.\kern 0.0
.\kern -633.0
.\hbox(0.0+0.0)x0.0
..\kern -72.26999
..\vbox(0.0+0.0)x345.0, glue set 72.26999fil
...\kern -72.26999
...\glue(\parskip) 0.0
...\hbox(0.0+0.0)x345.0, glue set 345.0fil
....\hbox(0.0+0.0)x0.0
....\hbox(0.0+0.0)x0.0
.....\hbox(0.0+0.0)x0.0
......\glue 0.0
......\hbox(0.0+794.96999)x0.0
.......\hbox(0.0+0.0)x0.0, shifted 794.96999
........\kern 0.0
........\glue 0.0 plus 1.0fil minus 1.0fil
......\glue 0.0 plus 1.0fil minus 1.0fil
....\penalty 10000
....\glue(\parfillskip) 0.0 plus 1.0fil
....\glue(\rightskip) 0.0
...\glue 0.0 plus 1.0fil minus 1.0fil
.\kern 633.0

It might not be that easy to see, but between top and intertext there is

...\glue 10.0 plus 2.0 minus 5.0
...\glue(\baselineskip) 4.72137

and between intertext and bottom there is

...\glue 10.0 plus 2.0 minus 5.0
...\glue(\baselineskip) 6.60004

These are the vertical skips inserted between the constructions. 10.0 plus 2.0 minus 5.0 both represent \abovedisplayskip and \belowdisplayskip which can stretch depending where the align fits within the regular text block construction. The definition of \intertext inside amsmath.dtx provides mention of these skips.

Soooooo... you can get rid of them using

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{align*}
  top \\[\dimexpr-\abovedisplayskip-\baselineskip]
  \intertext{intertext} \\[\dimexpr-\belowdisplayskip-\baselineskip]
  bottom
\end{align*}

\end{document}

However, if the intent is just to make a "comment on the left side of an equation", you could probably also do:

\documentclass{article}

\usepackage{amsmath}

\usepackage{zref-savepos,eso-pic}

\newcounter{lc}
\makeatletter
\newcommand{\leftcomment}[1]{%
  \stepcounter{lc}
  \ifmeasuring@\else
    \zsaveposx{comment-\thelc}% Current location x
  \fi
  \makebox[0pt][r]{%
    \makebox[\dimexpr\zposx{comment-\thelc}sp-\zposx{textblock}sp][l]{#1}%
  }
}
\makeatother

\AddToShipoutPictureBG*{\AtTextLowerLeft{\zsaveposx{textblock}}}% Left margin of text block

\begin{document}

\begin{align*}
  top \\[\dimexpr-\abovedisplayskip-\baselineskip]
  \intertext{intertext} \\[\dimexpr-\belowdisplayskip-\baselineskip]
  bottom
\end{align*}

\begin{align*}
                           f(x) &= ax^2 \leftcomment{intertext1} \\
  \leftcomment{intertext2} g(x) &= bx \tag{eq2}                  \\
                           h(x) &= c
\end{align*}

\end{document}

The idea being eso-pic is to capture the location of the text block left margin, while zref's savepos module allows us to capture the coordinate of a label using TeX's \label-\ref system. Since we use the latter, you'll have to compile twice with every change of the labels.

+1 for \showoutput and not falling back to TikZ to achieve just some positioning :-) — Daniel, Jan 06 '19 at 08:18
So I'm having trouble figuring out what is going on here. What is the final answer for \intertext? — user14554, Jan 06 '19 at 09:11
Note that your sample doesn't work correctly with the nccmath package, as requested by the OP. — siracusa, Jan 06 '19 at 12:10
Ok, so once again, could you explicitly state the exact, final spacing in pts? Because otherwise this just doesn't answer the question, it is much too convoluted when the answer should just be one number. — user14554, Jan 06 '19 at 19:32
Alright, thank you for your help and patience. Is there anything in particular that nccmath does? Does it add an extra 5pts or 3pts? Should it just be taken out entirely? All I remember ncc doing is adding the \fleqn, which I don't need if I can use \[-25pt] or flalign. — user14554, Jan 06 '19 at 19:47
@user14554: I couldn't resolve the vertical space with using nccmath, so I'm not sure. You can do without it, since amsmath provides fleqn and flalign. — Werner, Jan 06 '19 at 19:52
Do you know how "flush left" align somehow ends up forcing everything to align on the right-side of the page? That doesn't make sense to me if it is supposed to force text to be left-aligned. I guess it wasn't a solution after all. — user14554, Jan 06 '19 at 20:07
@user14554: You often have to add a & on the right-hand side. — Werner, Jan 06 '19 at 20:38
@user14554: It is actually 25pt plus 2pt minus 5pt in standard 10pt document, which means that the space can be stretched to up to 27pt and shrunk down to 20pt if this would improve the overall page layout. The distance between the \intertext line and the lines above/below it actually depends on other contents on the page. — Circumscribe, Jan 07 '19 at 11:38
@Werner: I think \glueexpr is more appropriate here than \dimexpr because with that the stretch will also be cancelled out. — Circumscribe, Jan 07 '19 at 11:41
In which location around or inside of an align environment do you use \glueexpr? — user14554, Jan 07 '19 at 22:11
@user14554: I don't use \glueexpr. Instead, I used \dimexpr. However, \abovedisplayskip and \belowdisplayskip are actually glue expressions that can shrink or expand, depending on the content of the document on the page the align appears in. Specifically, as Circumscribe mentions, \abovedisplayskip (and \belowdisplayskip) has a "length" of 10pt plus 2pt minus 5pt. So that "length" can be as short as 5pt (10pt minus 5pt) or as long as 12pt (10pt plus 2pt). \glueexpr keeps the "glue" (the plus and minus parts) while \dimexpr removes them... — Werner, Jan 07 '19 at 22:27
@user14554: ... you seemed interested in a fixed value rather than an explanation, hence my suggestion to use 25pt (which was 10pt for \abovedisplayskip/\belowdisplayskip without the glue + 15pt for \baselineskip). With the glue, it would be anything between 20pt (10pt + 15pt minus 5pt) and 27pt (10pt + 15pt plus 2pt). — Werner, Jan 07 '19 at 22:31
See the problem is it shouldn't be a "range" of values, my lines aren't in several places at once like some quantum superposition, it is one finite length, it should just be one value and then that's it. So all this glue and displayskip just doesn't help. — user14554, Jan 07 '19 at 22:57
@user14554: TeX was written with the optimal layout of paragraph and math content in mind. Lines are read in and than spacing is adjusted so that the typesetting is mathematically optimal. In order for this optimality to exist, some stretch is required between word, math content and other things so that adjustments can be made to improve the layout. It's an essential part of TeX. If you want to remove this, specifically for equations, then you can add \setlength{\abovedisplayskip}{\dimexpr\abovedisplayskip} (likewise for \belowdisplayskip and others) to your preamble... — Werner, Jan 07 '19 at 23:05
@user14554: ... it'll remove the "flexible spacing" that you loath. Removal of this in other areas within the document may result in bad alignment. Similar to comparing \raggedright with the regular typesetting of paragraphs (\justifying if you're using ragged2e). Of course, you're not forced to use (La)TeX... — Werner, Jan 07 '19 at 23:07

What is the vertical spacing caused by the \intertext or \shortintertext command?

1 Answers1