# How to put text below some text in an equation

Please refer the attached image. I want to write \omega \in \mathbb{R} below sup as shown in the equation in the image. How should I do it?

For what you want:

Er=\sup_{\omega\in\mathbb{R}}||G(j\omega)-R(j\omega)||_\infty


If you want to put arbitrary text (or anything) below some other text (or anything you want) generally you can use \underset{}{} and \mathop{} like this

%\usepackage{amsmath}
\underset{Under}{Normal}


or

\mathop{Normal}_{Under}


• Combining \underset and \mathop is a little redundant: either \underset{Under}{Normal} or \mathop{Normal}_{Under} would work, but for \lim-style operators \operatorname*{Normal} is advisable (or you could put \DeclareMathOperator*{\Normal}{Normal} in the preamble and then use \Normal). Note that \underset, \operatorname and \DeclareMathOperator all require amsmath. – Circumscribe Nov 16 '18 at 10:11
• (I just posted the answer because I use it :))) – user156344 Nov 16 '18 at 10:17
• No problem. Your answer is good, but you should remove \mathop in the second code block (it effectively does nothing) and you might want to mention that you need to load amsmath to use \underset. – Circumscribe Nov 16 '18 at 10:30
• @Circumscribe Actually I got it from Toogle TeX option of MathType one year ago when I am just a newbie to LaTeX. I always load amsmath package in all of my files, so I don't see any problem :) Thank you for give me more very useful knowledge! – user156344 Nov 16 '18 at 10:40
• Yeah, you'll probably always want to load amsmath if you're typesetting anything that that involves equations. While we're at it, it is better to use \| instead of || (because it is a single character), and better still to use \lVert and \rVert (also from amsmath) because these have better spacing. – Circumscribe Nov 16 '18 at 10:49