# How to fix the mismatch of font size of following?

I want to generate the cases in the picture. However, the Symbols T1, T2 on LHS and RHS are different in size.

\documentclass[a4paper, 12pt]{report}
\usepackage[utf8]{inputenc}
\usepackage[showframe]{geometry}
\usepackage{mathtools]

\begin{document}

\mbox{}
$$(\mathcal{T}_{1}, \mathcal{T}_{2})= \begin{cases} \frac{\left|\mathcal{T}_{1} \cap \mathcal{T}_{2}\right|}{Min\ {\left|\mathcal{T}_{1}\right|, \left|\mathcal{T}_{2}\right|\} } & negative~test, \\ -1 & positive~test \end{cases}$$
\end{document}


You can either set the \fraction using \displaystyle (via \dfrac), or use dcases. The latter provides a better solution since it results in better vertical spacing.

\documentclass{article}

\usepackage{mathtools}

\begin{document}

$(\mathcal{T}_1, \mathcal{T}_2) = \begin{dcases} \frac{| \mathcal{T}_1 \cap \mathcal{T}_2 |} {\min\{| \mathcal{T}_1 |, | \mathcal{T}_2 |\}} & \text{negative test}, \\ -1 & \text{positive test} \end{dcases}$

\end{document}

• In this case dcases* seems appropiate. – Manuel Nov 11 '18 at 8:58