Colab tutorials (#367)

* Colab Button & Run added

tutorials/tutorial6/tutorial.ipynb

@@ -7,6 +7,8 @@
    "source": [
     "# Tutorial: Building custom geometries with PINA `Location` class\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/tutorial6/tutorial.ipynb)\n",
+    "\n",
     "In this tutorial we will show how to use geometries in PINA. Specifically, the tutorial will include how to create geometries and how to visualize them. The topics covered are:\n",
     "\n",
     "* Creating CartesianDomains and EllipsoidDomains\n",
@@ -22,6 +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 matplotlib.pyplot as plt\n",
     "from pina.geometry import EllipsoidDomain, Difference, CartesianDomain, Union, SimplexDomain\n",
     "from pina.label_tensor import LabelTensor\n",