eqnarray (LaTeX2e unofficial reference manual (November 2018))

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### 8.8 `eqnarray`

The `eqnarray` environment is obsolete. It has infelicities, including spacing that is inconsistent with other mathematics elements. (See “Avoid eqnarray!” by Lars Madsen http://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*}

Unofficial LaTeX2e reference manual