[SPARK-16822][DOC] Support latex in scaladoc.

## What changes were proposed in this pull request?

Support using latex in scaladoc by adding MathJax javascript to the js template.

## How was this patch tested?

Generated scaladoc.  Preview:

- LogisticGradient: [before](https://spark.apache.org/docs/2.0.0/api/scala/index.html#org.apache.spark.mllib.optimization.LogisticGradient) and [after](https://sparkdocs.lins05.pw/spark-16822/api/scala/index.html#org.apache.spark.mllib.optimization.LogisticGradient)

- MinMaxScaler: [before](https://spark.apache.org/docs/2.0.0/api/scala/index.html#org.apache.spark.ml.feature.MinMaxScaler) and [after](https://sparkdocs.lins05.pw/spark-16822/api/scala/index.html#org.apache.spark.ml.feature.MinMaxScaler)

Author: Shuai Lin <linshuai2012@gmail.com>

Closes #14438 from lins05/spark-16822-support-latex-in-scaladoc.

1 files changed, 20 insertions, 0 deletions

diff --git a/docs/js/api-docs.js b/docs/js/api-docs.js
index ce89d8943b..96c63cc127 100644
--- a/docs/js/api-docs.js
+++ b/docs/js/api-docs.js
@@ -41,3 +41,23 @@ function addBadges(allAnnotations, name, tag, html) {
     .add(annotations.closest("div.fullcomment").prevAll("h4.signature"))
     .prepend(html);
 }
+
+$(document).ready(function() {
+  var script = document.createElement('script');
+  script.type = 'text/javascript';
+  script.async = true;
+  script.onload = function(){
+    MathJax.Hub.Config({
+      displayAlign: "left",
+      tex2jax: {
+        inlineMath: [ ["$", "$"], ["\\\\(","\\\\)"] ],
+        displayMath: [ ["$$","$$"], ["\\[", "\\]"] ],
+        processEscapes: true,
+        skipTags: ['script', 'noscript', 'style', 'textarea', 'pre', 'a']
+      }
+    });
+  };
+  script.src = ('https:' == document.location.protocol ? 'https://' : 'http://') +
+                'cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML';
+  document.getElementsByTagName('head')[0].appendChild(script);
+});