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\phantom
& \vphantom
& \hphantom
Synopsis:
\phantom{subformula}
or
\vphantom{subformula}
or
\hphantom{subformula}
The \phantom
command creates a box with the same height, depth,
and width as subformula, but empty. That is, this command causes
LaTeX to typeset the box but not its ink. The \vphantom
variant also produces an invisible box with the same height and depth as
subformula, but it has width zero. And \hphantom
makes a
box with the same width as subformula but with height and depth
zero.
Without the \vphantom
in this example, the top bars of the two
square roots would be at different heights.
\( \sqrt{\vphantom{a^3}a}\cdot\sqrt{a^3} \)
The \vphantom{a^3}
causes the first \sqrt
to have inside
it a box of the same height as the second \sqrt
, so LaTeX
makes the bars align.
These commands often are combined with \smash
. See \smash
for another example of the use of \vphantom
.
The three phantom commands appear often but note that LaTeX provides
a suite of other commands to work with box sizes that may be more
convenient, including \makebox
(see \mbox & \makebox) as well
as \settodepth
(see \settodepth), \settoheight
(see \settoheight), and \settowidth
(see \settowidth).
In addition, the mathtools package has many commands that offer
fine-grained control over spacing.
All three commands produce an ordinary box, without any special
mathematics status. So to do something like attaching a superscript you
should give it such a status, for example with the \operatorname
command from the package amsmath.
While most often used in mathematics, these three can appear in other
contexts. However, they don’t cause LaTeX to change into horizontal
mode. So if one of these starts a paragraph then you should prefix it
with \leavevmode
.