A simple liquid tag for Jekyll/Octopress that converts {% m %} and {% em %} into inline math, and {% math %} and {% endmath %} into block equations, by replacing with the appropriate MathJax script tags.

Jekyll nd Octopress Liquid tag for MathJax.rb

module Jekyll
  class MathJaxBlockTag < Liquid::Tag
    def render(context)
      '<script type="math/tex; mode=display">'
    end
  end
class MathJaxInlineTag < Liquid::Tag
    def render(context)
      '<script type="math/tex">'
    end
  end
class MathJaxEndTag < Liquid::Tag
    def render(context)
      '</script>'
    end
  end
end

Liquid::Template.register_tag('math', Jekyll::MathJaxBlockTag)
Liquid::Template.register_tag('m', Jekyll::MathJaxInlineTag)
Liquid::Template.register_tag('endmath', Jekyll::MathJaxEndTag)
Liquid::Template.register_tag('em', Jekyll::MathJaxEndTag)

Seems a problem: when '&' is used in block equations, it would cause a render error, as '&' is an illegal character in raw string.

Jekyll's default Markdown renderer has built in mathjax support: http://kramdown.gettalong.org/math_engine/mathjax.html