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I am trying to reproduce the following equation in LaTeX:

nopt(d, B) = argminn {Pt - LMI (d, n, ω + 0.5B) >= Pth }

and the syntax I have used is the following:

$n_{opt}\left(d, B\right) = argmin_n\lbraceP_t - L_{Mi}\left(d, n, \omega + 0.5B\right) \geq P_{th}\rbrace$

This does not compile and I get the

!Undefined Control Sequence Error.

Any suggestions on what I am missing here?

marked as duplicate by David Carlisle, ChrisS, Martin Schröder, Paul Gessler, Jesse Jan 27 '15 at 9:59

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  • 2
    Insert a space between \lbrace and P. (The error message you report receiving should indicate which control sequence -- here, \lbraceP -- is undefined. – Mico Jan 27 '15 at 8:49
  • 2
    It's the same mistake you did here: tex.stackexchange.com/q/224538/27635 – karlkoeller Jan 27 '15 at 9:01
up vote 3 down vote accepted

In addition to fixing the erroneous input that's causing LaTeX to report an undefined control sequence error, viz., the lack of a space in \lbraceP -- you should (a) set up argmin as a math operator and (b) render "opt" in upright-roman rather than in math-italic mode. Incidentally, the \left and \right directives don't resize the respective parentheses since the material they enclose isn't large; all they do is to insert unnecessary whitespace and contribute to a "loose" look of the equation. In short, don't use \left and \right here.

enter image description here

\documentclass{article}
\usepackage{amsmath}  % for \DeclareMathOperator macro
\DeclareMathOperator*{\argmin}{arg\,min}
\newcommand{\opt}{\mathrm{opt}}

\begin{document}
\[
n_{\opt}(d, B) = \argmin_n\bigl\lbrace P_t - L_{Mi}(d, n, \omega + 0.5B) \geq P_{th}\bigr\rbrace
\]
\end{document} 

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