Purpose

This post serves only to show the problem of Katex in fastpages. If the problem is solved, this post will be deleted.

Setting

I’m not touch anything in default setting for latest version of fastpage. Using displaystyle by using $$.

$$
\begin{aligned}
R^*=\underset{RR^t=I,\det(R)=1}{\operatorname{argmin}}\sum_{i=1}^n|RX_i-Y_i\|^2_2.
\end{aligned}
$$

This is rendered with default fastpage option in _config.yml; math_engine: null.

$$ \begin{aligned} R^*=\underset{RR^t=I,\det(R)=1}{\operatorname{argmin}}\sum_{i=1}^n|RX_i-Y_i\|^2_2. \end{aligned} $$

Problem

_config.yml is set as

kramdown:
  math_engine: katex
  input: GFM
  auto_ids: true
  hard_wrap: false
  syntax_highlighter: rouge

The result is

_config.yml is set as

kramdown:
  math_engine: null
  input: GFM
  auto_ids: true
  hard_wrap: false
  syntax_highlighter: rouge

The result is

The equation with katex option is not Italicized, and the font size is smaller than the one with null.