sum symbol in tikzposter too small

Question

I am using the tikzposter package and am fairly happy with it except for one small thing: When I have an equation with a sum the sum becomes ridiculously small.

I have read the questions about displaystyle vs textstyle and am using amsmath. Putting \displaystyle in front of \sum doesn't change anything.

Does anyone have any idea how to get a "normal" sum symbol?

MWE:

\documentclass[25pt, a0paper, portrait]{tikzposter}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage[T1]{fontenc} 
\usepackage{lmodern} 
\usepackage{amsmath}
\usepackage{amssymb}

\title{lalala}

\begin{document}
\maketitle

\block{test}{
  \begin{equation*}
    \Psi = \displaystyle\sum^{n_{max}}_{n=1}C_n
  \end{equation*}
}


\end{document}

Answer 1

It's a known bug of the Latin Modern fonts, which only supply the lmex font (extensible symbols) at a fixed size.

Note that this affects all “large symbols”, such as \sum, \int, \prod and so on, including extensible braces.

\documentclass[25pt, a0paper, portrait]{tikzposter}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage[T1]{fontenc} 
\usepackage{lmodern} 
\usepackage{amsmath}
\usepackage{amssymb}

% declare `cmex` to be arbitrary scalable
\DeclareFontShape{OMX}{cmex}{m}{n}{
  <-7.5> cmex7
  <7.5-8.5> cmex8
  <8.5-9.5> cmex9
  <9.5-> cmex10
}{}

\SetSymbolFont{largesymbols}{normal}{OMX}{cmex}{m}{n}
\SetSymbolFont{largesymbols}{bold}  {OMX}{cmex}{m}{n}

\title{lalala}

\begin{document}
\maketitle

\block{test}{
  \[
    \Psi = \sum^{n_{max}}_{n=1}C_n
  \]
}
\block{again}{
  \Huge
  \[
    \Psi = \sum^{n_{max}}_{n=1}C_n
  \]
}
\end{document}

Never use eqnarray.

Answer 2

The how about doing something like scaling the symbol and shifting it a bit to look nice. I know this is not a good practice, but for a poster it should do:

\documentclass[25pt, a0paper, portrait]{tikzposter}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage[T1]{fontenc} 
\usepackage{lmodern} 
\usepackage{amsmath}
\usepackage{amssymb}
\title{lalala}
\begin{document}
\maketitle
\block{test}{
  \begin{eqnarray*}
    \Psi = \displaystyle\raisebox{-10pt}{\scalebox{3.2}{\ensuremath{\sum}}}^{n_{max}}_{n=1}C_n
  \end{eqnarray*}
}
\end{document}

Remarks:

1. \scalebox{x}{y} scales the content y by factor x. It leaves math mode, so you need to enter it again.
2. \ensuremath{xx} enters math mode, either from normal text or from within math mode, i.e., you can always use \ensuremath, regardless whether in- or outside of math mode. (You cannot do that $). I used it here because initially, I forgot whether \scalebox would leave math mode or not.
3. \raisebox{x}{y} moves the contents of y up by x. In the poster, due to \scalebox, the sum symbol looked as if it was a bit too high in the formula, so I take it down by raising it a negative amount.