<p>For Corr, Cov and Var I usually use <code>\DeclareMathOperator{\Corr}{Corr}</code>, which, done once in an answer, allows me to just write <code>\Corr(X,Y)</code> whenever I need it later, which displays:</p>

<p>$$\DeclareMathOperator{\Corr}{Corr} \Corr(X,Y)$$</p>

<p>Like Amoeba's answer, this ensures spacing is done correctly in a way that <code>\mathrm</code> doesn't. But see <a href="https://tex.stackexchange.com/questions/67506/newcommand-vs-declaremathoperator">newcommand vs. DeclareMathOperator</a> on TEX.SE: Amoeba's answer apparently has the advantage that <code>newcommand</code> gives more flexibility.</p>

<p>But note I can still do <code>\DeclareMathOperator{\E}{\mathbb{E}} \E(X,Y)</code> and produce:</p>

<p>$$\DeclareMathOperator{\E}{\mathbb{E}} \E(X,Y)$$</p>

<p>And of course I can reuse these in a later piece of $\LaTeX$ too: $\E(X)+\Corr(X,Y)$</p>

<p>(In a document <code>DeclareMathOperator</code> <a href="https://tex.stackexchange.com/a/238272/25866">can only be used in a preamble</a> but this doesn't seem to cause any difficulty on here.)</p>
