[Tex/LaTex] Small product symbol in cases environment

Question

Suppose I would like to get this

MWE:

\documentclass{minimal}
\usepackage[cp1250]{inputenc}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\begin{document}

\begin{align*}
\prod
\end{align*}

\begin{align}
    \varphi (s) = T_n (s) =
    \begin{cases}
      \text{pro $n$ liché } & 2^{2m}s\prod\limits_{\mu = 1}^{m} (s^2 + \Omega_{0\mu}^2)\,,\ m = \frac{n - 1}{2} \\
      nn & nn     
    \end{cases}
\end{align}
\end{document}

First \prod symbol is there for comparison with the size of the \prod which is much smaller in cases environment below.

I would like to have same sized \prod symbol in cases like the bigger one.

Where is the problem? Is there any reason to not doing this?

Answer 1

The smaller \prod is in \textstyle (an inline style). You can override it by specifying \displaystyle prior to \prod. You will notice that the fraction {n-1}{2} also changes in size, again because of the difference between text style and display style math. The cases environment choses to set its cases in \textstyle.

\documentclass{minimal}
\usepackage[cp1250]{inputenc}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\begin{document}

\begin{align*}
\prod
\end{align*}

\begin{align}
    \varphi (s) = T_n (s) =
    \begin{cases}
      \text{pro $n$ liché } & 2^{2m}s\displaystyle\prod\limits_{\mu = 1}^{m} (s^2 + \Omega_{0\mu}^2)\,,\ m = \frac{n - 1}{2} \\
      nn & nn     
    \end{cases}
\end{align}
\end{document}