# Using MathJax in Category List Entries

Since the update of Octopress source code, this post won’t make sense anymore. I can’t find a way to use MathJax in category list entries anymore because category in plugins/category_generator.rb and plugins/category_list_tag.rb have both been changed to lower case. I don’t know how to track the Ruby code to revert it.

About three weeks ago, I successfully changed the category “LaTeX” to “$\rm \LaTeX$”.1 By trial, I discovered that $\rm \LaTeX$ should be input for “categories” at the head of the markdown source file of each Octopress post/page. Then, previewing the rendered contents at port 4000 at locolhost, I could see the category “$\rm \LaTeX$” rendered by MathJax at the bottom of each post/page. Moreover, in the category list in the sidebar at the right-hand side, the item “$\rm \LaTeX$” was also correctly displayed. However, as I clicked it, I was brought to a page which titled something similar to “Error 404”. Then, I realized that I need to modify the category list plugin2 so as to fix this error. I jotted the trailing part of wrong URL down: “-rm-latex-“.

Fortunately, the hyperlink for the category “$\rm \LaTeX$” at the bottom of each post was correct: $-slash-rm-slash-latex$. This was an important guide to what was going to be done to the category list plugin. As I am not going to spend most of my time to study IT, I aimed at merely changing “LaTeX” to “$\rm \LaTeX$”.

Viewing the source code of Watson’s category_list_tag.rb, I observed that the generated URL of each item in the category list was determined by the variable category_url, and the following method was responsible for the error.

category_url = File.join(category_dir, category.gsub(/_|\P{Word}/, '-').gsub(/-{2,}/, '-').downcase)


To solve the problem, I used the following approach:

1. Extract the trailing part of the URL of each category to category_string.
2. Use an if-statement to match category_string with the erroneous part URL: -rm-latex-.
• If it is not matched, then do nothing.
3. If it is matched, change the trailing part of category_url to $-slash-rm-slash-latex$.

That is, I added the following lines before writing the new item to the variable html.