4 3. DISPLAYED EQUATIONS
(Although the standard eqnarray environment remains available, it is better to
use align or equation+split instead. Within eqnarray, spacing around signs
of relation is not the preferred mathematical spacing, and is inconsistent with
that spacing as it appears in other environments. Long lines in this environment
may result in misplaced or overprinted equation numbers. This environment also
does not support the use of \qed or \qedhere as provided by theorem packages.)
Except for split, each environment has both starred and unstarred forms,
where the unstarred forms have automatic numbering using L
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X’s equation
counter. You can suppress the number on any particular line by putting \notag
before the end of that line; \notag should not be used outside a display environ-
ment as it will mess up the numbering. You can also override a number with a
tag of your own using \tag{hlabeli}, where hlabel i means arbitrary text such as
$*$ or ii used to “number” the equation. A tag can reference a different tagged
display by use of \tag{\ref{hlabel i}hmodifier i} where hmodifieri is optional.
If you are using hyperref, use \ref*; use of the starred form of \ref prevents a
reference to a modified tag containing a nested link from linking to the original
display.
There is also a \tag* command that causes the text you supply to be typeset
literally, without adding parentheses around it. \tag and \tag* can also be used
within the unnumbered versions of all the amsmath alignment structures. Some
examples of the use of \tag may be found in the sample files testmath.tex and
subeqn.tex provided with the amsmath package.
The split environment is a special subordinate form that is used only inside
one of the others. It cannot be used inside multline, however. split supports
only one alignment (&) column; if more are needed, aligned or alignedat
should be used. The width of a split structure is the full line width.
In the structures that do alignment (split, align and variants), relation
symbols have an & before them but not after—unlike eqnarray. Putting the
& after the relation symbol will interfere with the normal spacing; it has to go
before.
In all multiline environments, lines are divided by \\. The \\ should not be
used to end the last line. Using it there will result in unwanted extra vertical
space following the display.
In all math environments (inline or display), blank lines (equivalent to \par)
are not permitted, and will result in an error.
3.2 Single equations
The equation environment is for a single equation with an automatically gen-
erated number. The equation* environment is the same except for omitting
the number.
1
The wrapper \[ ... \] is equivalent to equation*.
3.3 Split equations without alignment
The multline environment is a variation of the equation environment used for
equations that don’t fit on a single line. The first line of a multline will be at
1
Basic L
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alent environment named displaymath.