### Section 4.11.1

The `rowSums` formula should read

\[

\mathbf{A1}=\sum_{i}^{n}\mathbf{A}_{*i},

\]

and the `colSums` formula should read

\[

\mathbf{A}^{\top}\mathbf{1}=\sum_{i}^{m}\mathbf{A}_{i*}

\]

**Note:**it is a little bit confusing. Following R semantics, the rowSums() method means "row-wise sum" which is the same as "sum of columns"; and vice versa, the colSums() method means "column-wise sum", which can be computed as the sum of matrix rows.

### Section 6.1

The dimensions of matrix $$\mathbf{V}$$ are $$\mathbf{V}\in\mathbb{R}^{n\times k}$$.Formula (6.1) should read

\[

\begin{equation}

\boldsymbol{a}_{pca}=\mathbf{V}^{\top}\left(\boldsymbol{a}-\boldsymbol{\mu}\right).\label{eq:to-pca}

\end{equation}

\]

Formula (6.2) - (6.3) should read

\[

\begin{eqnarray}

\boldsymbol{a} & = & \left(\mathbf{V}^{\top}\right)^{\text{-}1}\boldsymbol{a}_{pca}+\boldsymbol{\mu} \\

& = & \mathbf{V}\boldsymbol{a}_{pca}+\boldsymbol{\mu}.\label{eq:from-pca}

\end{eqnarray}

\]

3/12/2016

### Section 8.3

In Step (1): Setup working directories and acquire data, the URL of the Wikipedia XML dump has since changed. The third command of Step (1) should read:

curl http://dumps.wikimedia.org/enwiki/latest/enwiki-latest-pages-articles10.xml-p002336425p003046511.bz2 -o $WORK_DIR/wikixml/enwiki-latest-pages-articles.xml.bz2

We keep the Kindle edition updated with the Errata. If you have ever bought the print version from Amazon, the Kindle version is free via Amazon MatchBook. If you already have a Kindle version, you should be able just to reload it with the updated one.