\documentclass{article}

\providecommand{\optionswitch}{0}

\ifcase\optionswitch
  % no package
\else
  \typeout{Using concmath}
  \usepackage{concmath}
\fi

\thispagestyle{empty}

\def\maths{%
\hat f({\bf g})\approx\sqrt{\left\lfloor\int_0^1\frac{\cos\omega}{\varphi^2_i}\,{\rm d}y\right\}
}}

\begin{document}
$\maths \to \displaystyle\maths$
\end{document}
