make superscript show up correctly in doc

mllib/src/main/scala/org/apache/spark/mllib/linalg/distributed/RowMatrix.scala

@@ -254,12 +254,12 @@ class RowMatrix(
    * We assume n is smaller than m. The singular values and the right singular vectors are derived
    * from the eigenvalues and the eigenvectors of the Gramian matrix A' * A. U, the matrix
    * storing the right singular vectors, is computed via matrix multiplication as
-   * U = A * (V * S^{-1}), if requested by user. The actual method to use is determined
+   * U = A * (V * S^-1^), if requested by user. The actual method to use is determined
    * automatically based on the cost:
    *  - If n is small (n < 100) or k is large compared with n (k > n / 2), we compute the Gramian
    *    matrix first and then compute its top eigenvalues and eigenvectors locally on the driver.
-   *    This requires a single pass with O(n^2) storage on each executor and on the driver, and
-   *    O(n^2 k) time on the driver.
+   *    This requires a single pass with O(n^2^) storage on each executor and on the driver, and
+   *    O(n^2^ k) time on the driver.
    *  - Otherwise, we compute (A' * A) * v in a distributive way and send it to ARPACK's DSAUPD to
    *    compute (A' * A)'s top eigenvalues and eigenvectors on the driver node. This requires O(k)
    *    passes, O(n) storage on each executor, and O(n k) storage on the driver.