If you want "limits" of this operator, e.g., x\in A
, always to be typeset as a "subscript" (to the right and below the "E") rather than entirely below the "E" when in display math mode, you may want to use the \DeclareMathOperator
instruction that is made available by loading the amsmath
or amsopn
packages.
Aside: The \mathop
directive, in contrast, will make its argument behave exactly like \sum
or \prod
, in the sense that subscript and superscript arguments will be typeset fully below or above the operator when the directive is processed in display-math mode. Do check out @DavidCarlisle's answer for an application of the \mathop
directive to your case.
\documentclass{article}
\usepackage{amsmath,amssymb}
\DeclareMathOperator{\E}{\mathbb{E}}
\begin{document}
$\E_{x\in A}$ and $\displaystyle \E_{x\in A}$
vs.\ $\displaystyle \mathop{\mathbb{E}}_{x\in A}$
\end{document}

Conversely, if you do want the x\in A
particle to be typeset entirely below the operator when TeX is in display-math mode, you could use the instruction \DeclareMathOperator*
(note the *
) instead: \DeclareMathOperator*{\E}{\mathbb{E}}
.
$$
in LaTeX.