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<head>
<title>UK TeX FAQ -- question label newfunction</title>
</head><body>
<h3>Defining a new log-like function in LaTeX</h3>
<p/>Use the <code>\</code><code>mathop</code> command, as in:
<blockquote>
<pre>
\newcommand{\diag}{\mathop{\mathrm{diag}}}
</pre>
</blockquote><p>
<p/>Subscripts and superscripts on <code>\</code><code>diag</code> will be placed below and
above the function name, as they are on
<code>\</code><code>lim</code>. If you want your subscripts and superscripts always placed
to the right, do:
<blockquote>
<pre>
\newcommand{\diag}{\mathop{\mathrm{diag}}\nolimits}
</pre>
</blockquote><p>
<p/>AMSLaTeX (in its <i>amsopn</i> package, which is automatically
loaded by <i>amsmath</i>) provides a command
<code>\</code><code>DeclareMathOperator</code> that takes does the same job as the first
definition above. To create our original <code>\</code><code>diag</code> command, one would
say:
<blockquote>
<pre>
\DeclareMathOperator{\diag}{diag}
</pre>
</blockquote><p>
<code>\</code><code>DeclareMathOperator*</code> declares the operator always to have its
sub- and superscripts in the
“<a href="FAQ-limits.html"><code>\</code><code>limits</code> position</a>”.
<p/>The <i>amsopn</i> command <code>\</code><code>operatorname</code> allows you to
introduce <em>ad hoc</em> operators into your mathematics, so
<blockquote>
<code>\</code><code>[</code> <code>\</code><code>operatorname{foo}</code><code>(bar)</code> <code>\</code><code>]</code>
</blockquote><p>
typesets the same as
<blockquote>
<pre>
\DeclareMathOperator{\foo}{foo}
...
\[ \foo(bar) \]
</pre>
</blockquote><p>
As with <code>\</code><code>DeclareMathOperator</code> there’s a starred version
<code>\</code><code>operatorname*</code> for sub- and superscripts in the limits position.
<p/>(It should be noted that “log-like” was reportedly a <em>joke</em> on
Lamport’s part; it is of course clear what was meant.)
<dl>
<dt><tt><i>amsopn.sty</i></tt><dd>In the AMSLaTeX distribution <a href="http://www.tex.ac.uk/www.tex.ac.uk tex-archive/macros/latex/required/amslatex.zip">macros/latex/required/amslatex</a> (or <a href="http://www.tex.ac.uk/www.tex.ac.uk tex-archive/macros/latex/required/amslatex/">browse the directory</a>)
</dl>
<p/><p>This question on the Web: <a href="http://www.tex.ac.uk/cgi-bin/texfaq2html?label=newfunction">http://www.tex.ac.uk/cgi-bin/texfaq2html?label=newfunction</a>
</body>
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