minor updates

Author: atcemgil

Automatic Differentiation.ipynb

@@ -6,7 +6,9 @@
    "source": [
     "# Automatic differentiation\n",
     "\n",
-    "__Automatic differentiation__ is a method for evaluating the rate of change in the numerical output of a program with respect to the rate of change in its input. We start with an example.\n",
+    "__Automatic differentiation__ is a method for evaluating the rate of change in the numerical output of a program with respect to the rate of change in its input. The power of the method is the ability of writing a program that computes a differentiable function and having the derivative immediatelly available.\n",
+    "\n",
+    "We start with an example.\n",
     "\n",
     "Consider the function\n",
     "$$\n",