\int_{\mathbb R^D} \Delta S \cdot S \, dx
= -\int_{\mathbb R^D} \nabla S\cdot \nabla S\, dx
= \mean{(\nabla S)^2}
我想写上平均符号,$(\nabla S)^2$
但是它不起作用。我该如何写?
答案1
你可能的意思是:
\int_{\mathbb R^D} \Delta S \cdot S \, dx
= -\int_{\mathbb R^D} \nabla S\cdot \nabla S\, dx
= \overline{(\nabla )^2 S}
或者,正如评论中所建议的那样
\documentclass{article}
\usepackage{amsmath,amssymb}
\begin{document}
\def\mean#1{\left< #1 \right>}
\[
\int_{\mathbb R^D} \Delta S \cdot S \, dx = -\int_{\mathbb R^D} \nabla S\cdot \nabla S\, dx = \mean{(\nabla S)^2}
\]
\end{document}
结果如下: