Revert "More clear and intuitive math explanation"

Author: apaszke

Deep Learning with PyTorch.ipynb

@@ -426,7 +426,7 @@
    "source": [
     "You should have got a matrix of `4.5`.\n",
     "Let's call the `out` *Variable* \"$o$\".  \n",
-    "We have that $o = \\frac{1}{4}\\sum_i z_i$, $z_i = \\frac{3}{4}(x_i+2)^2$ and $z_i\\bigr\\rvert_{x_i=1} = 27$. Therefore, $\\frac{\\partial o}{\\partial x_i} = \\frac{6}{4}(x_i+2)$, hence $\\frac{\\partial o}{\\partial x_i}\\bigr\\rvert_{x_i=1} = \\frac{18}{4} = 4.5$."
+    "We have that $o = \\frac{1}{4}\\sum_i z_i$, $z_i = 3(x_i+2)^2$ and $z_i\\bigr\\rvert_{x_i=1} = 27$. Therefore, $\\frac{\\partial o}{\\partial x_i} = \\frac{3}{2}(x_i+2)$, hence $\\frac{\\partial o}{\\partial x_i}\\bigr\\rvert_{x_i=1} = \\frac{9}{2} = 4.5$."
    ]
   },
   {
@@ -1261,7 +1261,6 @@
   }
  ],
  "metadata": {
-  "anaconda-cloud": {},
   "kernelspec": {
    "display_name": "Python 2",
    "language": "python",