[MINOR][ML] Fix some mistake in LinearRegression formula.

## What changes were proposed in this pull request?
Fix some mistake in ```LinearRegression``` formula.

## How was this patch tested?
Documents change, no tests.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #14369 from yanboliang/LiR-formula.

1 files changed, 3 insertions, 3 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala b/mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala
index a0ff7f07aa..f3dc65e0df 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala
@@ -800,16 +800,16 @@ class LinearRegressionSummary private[regression] (
  * {{{
  * \frac{\partial L}{\partial w_i} =
  *     1/N \sum_j diff_j (x_{ij} - \bar{x_i}) / \hat{x_i}
- *   = 1/N ((\sum_j diff_j x_{ij} / \hat{x_i}) - diffSum \bar{x_i}) / \hat{x_i})
+ *   = 1/N ((\sum_j diff_j x_{ij} / \hat{x_i}) - diffSum \bar{x_i} / \hat{x_i})
  *   = 1/N ((\sum_j diff_j x_{ij} / \hat{x_i}) + correction_i)
  * }}},
- * where correction_i = - diffSum \bar{x_i}) / \hat{x_i}
+ * where correction_i = - diffSum \bar{x_i} / \hat{x_i}
  *
  * A simple math can show that diffSum is actually zero, so we don't even
  * need to add the correction terms in the end. From the definition of diff,
  * {{{
  * diffSum = \sum_j (\sum_i w_i(x_{ij} - \bar{x_i}) / \hat{x_i} - (y_j - \bar{y}) / \hat{y})
- *         = N * (\sum_i w_i(\bar{x_i} - \bar{x_i}) / \hat{x_i} - (\bar{y_j} - \bar{y}) / \hat{y})
+ *         = N * (\sum_i w_i(\bar{x_i} - \bar{x_i}) / \hat{x_i} - (\bar{y} - \bar{y}) / \hat{y})
  *         = 0
  * }}}
  *