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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`

.