Add autodiff demos

Author: benmarlin

autodiff_demos.ipynb

@@ -361,6 +361,34 @@
     "w.backward()\n",
     "print(\"Autodiff:\", x1.grad, x2.grad,\"\\n\")\n"
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "impurity=[]\n",
+    "argmin=[]\n",
+    "R=0"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def getsplit(X,Y):\n",
+    "    I = impurity(Y)\n",
+    "    for i in range(X.shape[1]):\n",
+    "        for t in X[:i]: \n",
+    "            ind = X[:,i] >= t\n",
+    "            R[i,t] = I - (impurity(Y[ind]) + impurity(Y[~ind]))\n",
+    "    i, t = argmin(R)\n",
+    "    ind = X[:,i] >= t\n",
+    "    return(i,t,(X[ind,:], Y[ind]), (X[~ind,:], Y[~ind]))"
+   ]
   }
  ],
  "metadata": {