added space after operator

Example code was missing a space after the @ operator

Author: rlabbe

13-Smoothing.ipynb

@@ -268,7 +268,7 @@
     "    for k in range(n-2,-1,-1):\n",
     "        Pp[k] = F @ P[k] @ F.T + Q # predicted covariance\n",
     "\n",
-    "        K[k]  = P[k] @ F.T @inv(Pp[k])\n",
+    "        K[k]  = P[k] @ F.T @ inv(Pp[k])\n",
     "        x[k] += K[k] @ (x[k+1] - (F @ x[k]))     \n",
     "        P[k] += K[k] @ (P[k+1] - Pp[k]) @ K[k].T\n",
     "    return (x, P, K, Pp)\n",