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`eqnarray`

The `eqnarray`

environment is obsolete. It has infelicities,
including spacing that is inconsistent with other mathematics elements.
(See “Avoid eqnarray!” by Lars Madsen
https://tug.org/TUGboat/tb33-1/tb103madsen.pdf). New documents
should include the `amsmath` package and use the displayed
mathematics environments provided there, such as the `align`

environment. We include a description only for completeness and for
working with old documents.

Synopsis:

\begin{eqnarray}first formula left&first formula middle&first formula right\\ ... \end{eqnarray}

or

\begin{eqnarray*}first formula left&first formula middle&first formula right\\ ... \end{eqnarray*}

Display a sequence of equations or inequalities. The left and right sides are typeset in display mode, while the middle is typeset in text mode.

It is similar to a three-column `array`

environment, with items
within a row separated by an ampersand (`&`

), and with rows
separated by double backslash `\\`

).
The starred form of line break (`\\*`

) can also be used to separate
equations, and will disallow a page break there (see \\).

The unstarred form `eqnarray`

places an equation number on every
line (using the `equation`

counter), unless that line contains a
`\nonumber`

command. The starred form `eqnarray*`

omits
equation numbering, while otherwise being the same.

The command `\lefteqn`

is used for splitting long formulas across
lines. It typesets its argument in display style flush left in a box of
zero width.

This example shows three lines. The first two lines make an inequality, while the third line has not entry on the left side.

\begin{eqnarray*} \lefteqn{x_1+x_2+\cdots+x_n} \\ &\leq &y_1+y_2+\cdots+y_n \\ &= &z+y_3+\cdots+y_n \end{eqnarray*}