Colab tutorials (#367)

* Colab Button & Run added

tutorials/tutorial9/tutorial.ipynb

@@ -5,6 +5,9 @@
    "metadata": {},
    "source": [
     "# Tutorial: One dimensional Helmholtz equation using Periodic Boundary Conditions\n",
+    "\n",
+    "[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/mathLab/PINA/blob/master/tutorials/tutorial9/tutorial.ipynb)\n",
+    "\n",
     "This tutorial presents how to solve with Physics-Informed Neural Networks (PINNs)\n",
     "a one dimensional Helmholtz equation with periodic boundary conditions (PBC).\n",
     "We will train with standard PINN's training by augmenting the input with\n",
@@ -21,6 +24,15 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "## routine needed to run the notebook on Google Colab\n",
+    "try:\n",
+    "  import google.colab\n",
+    "  IN_COLAB = True\n",
+    "except:\n",
+    "  IN_COLAB = False\n",
+    "if IN_COLAB:\n",
+    "  !pip install \"pina-mathlab\"\n",
+    "\n",
     "import torch\n",
     "import matplotlib.pyplot as plt\n",
     "\n",