Add intro paragraph, tx to Daniel and minor formatting fixes

extra_gradient_descent_comparison.ipynb

@@ -1,5 +1,19 @@
 {
  "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Comparison of Batch, Mini-Batch and Stochastic Gradient Descent"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "This notebook displays an animation comparing Batch, Mini-Batch and Stochastic Gradient Descent (introduced in Chapter 4). Thanks to [Daniel Ingram](https://github.com/daniel-s-ingram) who contributed this notebook."
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": 1,
@@ -159,7 +173,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 15,
+   "execution_count": 11,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -174,7 +188,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 16,
+   "execution_count": 12,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -202,23 +216,30 @@
     "    cost_ax.set_ylim([0, 5])\n",
     "\n",
     "    data_ax.set_xlabel(r'$x_1$')\n",
-    "    data_ax.set_ylabel(r'$y$')\n",
+    "    data_ax.set_ylabel(r'$y$', rotation=0)\n",
     "    cost_ax.set_xlabel(r'$\\theta_0$')\n",
     "    cost_ax.set_ylabel(r'$\\theta_1$')\n",
     "\n",
-    "    data_ax.legend(('Data', 'BGD', 'SGD', 'MBGD'))\n",
-    "    cost_ax.legend(('Normal Equation', 'BGD', 'SGD', 'MBGD'))"
+    "    data_ax.legend(('Data', 'BGD', 'SGD', 'MBGD'), loc=\"upper left\")\n",
+    "    cost_ax.legend(('Normal Equation', 'BGD', 'SGD', 'MBGD'), loc=\"upper left\")"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 13,
    "metadata": {},
    "outputs": [],
    "source": [
     "animation = FuncAnimation(fig, animate, frames=n_iter)\n",
     "plt.show()"
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
   }
  ],
  "metadata": {
@@ -237,7 +258,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.5.2"
+   "version": "3.6.6"
   }
  },
  "nbformat": 4,