change typo and fix equation ref

Author: shuanghuab

local_optimization/NLDF/data_fitting_robustness.ipynb

@@ -16,7 +16,7 @@
     "## Technical Setup\n",
     "\n",
     "### NAG Library\n",
-    "To run this notebook, you will need to install the NAG Library for Python (Mark 28.5 or newer) and a license key. You can find the software and request key from our website here: https://www.nag.com/content/getting-started-nag-library?lang=py&os=linux\n",
+    "To run this notebook, you will need to install the NAG Library for Python (Mark 28.5 or newer) and a license key. You can find the software and request a license key from our website here: https://www.nag.com/content/getting-started-nag-library?lang=py&os=linux\n",
     "\n",
     "### Correct Rendering of this notebook\n",
     "\n",
@@ -108,7 +108,6 @@
     "We will fit it with a model \n",
     "\n",
     "$$\n",
-    "\\label{model}\n",
     "\\varphi(t;x)\\ =x_1\\sin(x_2t)\n",
     "$$\n",
     "\n",
@@ -452,7 +451,7 @@
    "id": "7e721f62",
    "metadata": {},
    "source": [
-    "We will fit this data set using 3 different loss functions with the same model $\\varphi(t;x)$ defined in (\\ref{model}) each time and discuss the results under the plots all at once below."
+    "We will fit this data set using 3 different loss functions with the same model $\\varphi(t;x)$ each time and discuss the results under the plots all at once below."
    ]
   },
   {