diff --git a/doc/ipython-notebooks/clustering/GMM.ipynb b/doc/ipython-notebooks/clustering/GMM.ipynb
index a9dd08d0d27..d282ebf23ab 100644
--- a/doc/ipython-notebooks/clustering/GMM.ipynb
+++ b/doc/ipython-notebooks/clustering/GMM.ipynb
@@ -1,6 +1,7 @@
 {
  "metadata": {
-  "name": ""
+  "name": "",
+  "signature": "sha256:2360184c5183480d9a2f8ce3f73ed3c929a0ada3429ecb95ee828fa9ae5e98a8"
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  "nbformat": 3,
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diff --git a/doc/ipython-notebooks/pca/pca_notebook.ipynb b/doc/ipython-notebooks/pca/pca_notebook.ipynb
index e282c6c590a..0ec06248dea 100644
--- a/doc/ipython-notebooks/pca/pca_notebook.ipynb
+++ b/doc/ipython-notebooks/pca/pca_notebook.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:3d13daedde9c7640249c0cb0983d00d6519b14626cee436879a4b5208e5b14a6"
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  "nbformat": 3,
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@@ -28,7 +28,7 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "This notebook is about finding Principal Components of data (Unsupervised). It's dimensional reduction capabilities are further utilised to show it's application in data compression, image processing and face recognition. "
+      "This notebook is about finding Principal Components (<a href=\"http://en.wikipedia.org/wiki/Principal_component_analysis\">PCA</a>) of data (<a href=\"http://en.wikipedia.org/wiki/Unsupervised_learning\">Unsupervised</a>). It's <a href=\"http://en.wikipedia.org/wiki/Dimensionality_reduction\">dimensional reduction</a> capabilities are further utilised to show it's application in <a href=\"http://en.wikipedia.org/wiki/Data_compression\">data compression</a>, image processing and <a href=\"http://en.wikipedia.org/wiki/Facial_recognition_system\">face recognition</a>. "
      ]
     },
     {