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0113 <a name="array"></a>
0114 <div class="header">
0115 <p>
0116 Next: <a href="center.html#center" accesskey="n" rel="next">center</a>, Previous: <a href="abstract.html#abstract" accesskey="p" rel="prev">abstract</a>, Up: <a href="Environments.html#Environments" accesskey="u" rel="up">Environments</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="IndexDocument.html#Index" title="Index" rel="index">Index</a>]</p>
0117 </div>
0118 <hr>
0119 <a name="array-1"></a>
0120 <h3 class="section">8.2 <code>array</code></h3>
0121 
0122 <a name="index-environment_002c-array"></a>
0123 <a name="index-array-environment"></a>
0124         
0125 <a name="index-arrays_002c-math"></a>
0126 
0127 <p>Synopsis:
0128 </p>
0129 <div class="example">
0130 <pre class="example">\begin{array}{<var>cols</var>}
0131   <var>column 1 entry</var> &amp;<var>column 2 entry</var> ... &amp;<var>column n entry</var> \\
0132   ...
0133 \end{array}
0134 </pre></div>
0135 
0136 <p>or:
0137 </p>
0138 <div class="example">
0139 <pre class="example">\begin{array}[<var>pos</var>]{<var>cols</var>}
0140   <var>column 1 entry</var> &amp;<var>column 2 entry</var> ... &amp;<var>column n entry</var> \\
0141   ...
0142 \end{array}
0143 </pre></div>
0144 
0145 <p>Produce a mathematical array.  This environment can only be used in math
0146 mode, and normally appears within a displayed mathematics environment
0147 such as <code>equation</code> (see <a href="equation.html#equation">equation</a>).  Inside of each row the
0148 column entries are separated by an ampersand, (<code>&amp;</code>).  Rows are
0149 terminated with double-backslashes (see <a href="_005c_005c.html#g_t_005c_005c">\\</a>).
0150 </p>
0151 <p>This example shows a three by three array.
0152 </p>
0153 <div class="example">
0154 <pre class="example">\begin{equation*}
0155   \chi(x) =
0156   \left|              % vertical bar fence
0157     \begin{array}{ccc}
0158       x-a  &amp;-b  &amp;-c  \\
0159       -d   &amp;x-e &amp;-f  \\
0160       -g   &amp;-h  &amp;x-i
0161     \end{array}
0162  \right|
0163 \end{equation*}
0164 </pre></div>
0165 
0166 <p>The required argument <var>cols</var> describes the number of columns, their
0167 alignment, and the formatting of the intercolumn regions.  For instance,
0168 <code>\begin{array}{rcl}...\end{array}</code> gives three columns: the
0169 first flush right, the second centered, and the third flush left.  See
0170 <a href="tabular.html#tabular">tabular</a> for the complete description of <var>cols</var> and of the
0171 other common features of the two environments, including the optional
0172 <var>pos</var> argument.
0173 </p>
0174 <p>There are two ways that <code>array</code> diverges from <code>tabular</code>.  The
0175 first is that <code>array</code> entries are typeset in math mode, in
0176 textstyle (see <a href="Modes.html#Modes">Modes</a>) except if the <var>cols</var> definition specifies
0177 the column with <code>p{...}</code>, which causes the entry to be typeset in
0178 text mode.  The second is that, instead of <code>tabular</code>&rsquo;s parameter
0179 <code>\tabcolsep</code>, LaTeX&rsquo;s intercolumn space in an <code>array</code> is
0180 governed by
0181 <a name="index-_005carraycolsep"></a>
0182 <code>\arraycolsep</code>, which gives half the width between columns. The
0183 default for this is &lsquo;<samp>5pt</samp>&rsquo; so that between two columns comes
0184 10pt of space.
0185 </p>
0186 <a name="index-package_002c-amsmath"></a>
0187 <a name="index-amsmath-package"></a>
0188 
0189 <p>To obtain arrays with braces the standard is to use the <samp>amsmath</samp>
0190 package.  It comes with environments <code>pmatrix</code> for an array
0191 surrounded by parentheses&nbsp;<code>(...)</code>, <code>bmatrix</code> for an array
0192 surrounded by square brackets&nbsp;<code>[...]</code>, <code>Bmatrix</code> for an
0193 array surrounded by curly braces&nbsp;<code>{...}</code>, <code>vmatrix</code> for
0194 an array surrounded by vertical bars&nbsp;<code>|...|</code>, and
0195 <code>Vmatrix</code> for an array surrounded by double vertical
0196 bars&nbsp;<code>||...||</code>, along with a number of other array constructs.
0197 </p>
0198 <a name="index-package_002c-amsmath-1"></a>
0199 <a name="index-amsmath-package-1"></a>
0200 
0201 <p>The next example uses the <samp>amsmath</samp> package.
0202 </p>
0203 <div class="example">
0204 <pre class="example">\usepackage{amsmath}  % in preamble
0205 
0206 \begin{equation}    
0207   \begin{vmatrix}{cc}  % array with vert lines
0208     a  &amp;b \\
0209     c  &amp;d       
0210   \end{vmatrix}=ad-bc
0211 \end{equation}
0212 </pre></div>
0213 
0214 <a name="index-package_002c-array-_0028package_0029"></a>
0215 <a name="index-array-_0028package_0029-package"></a>
0216 
0217 <a name="index-package_002c-dcolumn"></a>
0218 <a name="index-dcolumn-package"></a>
0219 
0220 <p>There are many packages concerning arrays.  The <samp>array</samp> package has
0221 many useful extensions, including more column types.  The <samp>dcolumn</samp>
0222 package adds a column type to center on a decimal point.  For both see
0223 the documentation on CTAN.
0224 </p>
0225 
0226 
0227 
0228 <hr/><div class='referenceinfo'> <a href='https://latexref.xyz/'> <i>Unofficial LaTeX2e reference manual</i></a></div>
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