diff --git a/01_introduction.ipynb b/01_introduction.ipynb
index f66e1b6637e275d173e7be32b2c230d02b08f427..77c79ea3d643fdec70c62eee03d8f2f17bbf3853 100644
--- a/01_introduction.ipynb
+++ b/01_introduction.ipynb
@@ -425,6 +425,13 @@
     "</div>"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<img src=\"images/feature_matrix.png\" width=50%/>"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -651,6 +658,17 @@
     "print(\"image_vector:\", image_vector)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<br/>\n",
+    "\n",
+    "This is how the final feature matrix then looks like:\n",
+    "\n",
+    "<img src=\"images/feature_matrix_mnist.png\" width=50%/>"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -662,7 +680,9 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "If we start a machine learning project for texts, we first have to choose a dictionary (a set of words) for this project. The words in the dictionary are enumerated. The final representation of a text as a feature vector depends on this dictionary.\n",
+    "- If we start a machine learning project for texts, we first have to choose a dictionary (a set of words) for this project. \n",
+    "- The words in the dictionary are enumerated. \n",
+    "- The final representation of a text as a feature vector depends on this dictionary.\n",
     "\n",
     "Such a dictionary can be very large, but for the sake of simplicity we use a very small enumerated dictionary to explain the overall procedure:\n",
     "\n",
@@ -741,6 +761,15 @@
     "print(vector)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<br/>\n",
+    "The corresponding feautre matrix then has the form:\n",
+    "<img src=\"images/feature_matrix_document.png\" width=70% />"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -1825,6 +1854,7 @@
  ],
  "metadata": {
   "celltoolbar": "Tags",
+  "hide_input": false,
   "kernelspec": {
    "display_name": "Python 3",
    "language": "python",
@@ -1840,7 +1870,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.2"
+   "version": "3.7.4"
   },
   "latex_envs": {
    "LaTeX_envs_menu_present": true,
@@ -1873,12 +1903,12 @@
     "height": "calc(100% - 180px)",
     "left": "10px",
     "top": "150px",
-    "width": "288px"
+    "width": "178.6666717529297px"
    },
    "toc_section_display": true,
    "toc_window_display": true
   }
  },
  "nbformat": 4,
- "nbformat_minor": 2
+ "nbformat_minor": 4
 }
diff --git a/images/activate_cell_meta.png b/images/activate_cell_meta.png
new file mode 100644
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diff --git a/images/feature_matrix.png b/images/feature_matrix.png
new file mode 100644
index 0000000000000000000000000000000000000000..4bbad471ffbe8592e6694df26bfbeaeed6cd4b79
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diff --git a/images/feature_matrix.pptx b/images/feature_matrix.pptx
new file mode 100644
index 0000000000000000000000000000000000000000..a741b014239e0052544850d09ff713090fb42f0a
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diff --git a/images/feature_matrix_document.png b/images/feature_matrix_document.png
new file mode 100644
index 0000000000000000000000000000000000000000..5ab0e8dad4085ccdd06f651a06fef6452f8c19ad
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diff --git a/images/feature_matrix_document.pptx b/images/feature_matrix_document.pptx
new file mode 100644
index 0000000000000000000000000000000000000000..1fd0c77b30c8e2fbd9f86051e9ff63afd2c0c1cd
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diff --git a/images/feature_matrix_mnist.png b/images/feature_matrix_mnist.png
new file mode 100644
index 0000000000000000000000000000000000000000..902c3f4c164434a42f033487d6cf0f92e1113b51
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diff --git a/images/feature_matrix_mnist.pptx b/images/feature_matrix_mnist.pptx
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