Docs: Improve tutorials by adding basic analysis functions

docs/source/tutorials/1_Introduction-to-the-API.ipynb

@@ -94,6 +94,25 @@
     "ts = OpenPMDTimeSeries('./example-2d/hdf5/')"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Extracting iterations and time values\n",
+    "\n",
+    "One can extract all available iterations and corresponding time values from the time series into a numpy array object by doing"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "it = ts.iterations\n",
+    "time = ts.t"
+   ]
+  },
   {
    "attachments": {},
    "cell_type": "markdown",
@@ -103,6 +122,8 @@
     "\n",
     "### Accessing the field data\n",
     "\n",
+    "The list of available fields is accessible through `ts.avail_fields`.\n",
+    "\n",
     "The fields can be read with the method `get_field`. \n",
     "\n",
     "The user can either require a time (in seconds) or an iteration (an integer). When giving a time, it is not needed to provide the exact time of an available iteration, as the time of the closest available value will be used instead."
@@ -127,7 +148,7 @@
    "source": [
     "The method `get_field` returns two quantities:\n",
     "- A 2D array containing the values of the requested field.\n",
-    "- A object containing metainformation about the extent of the grid.\n",
+    "- An object containing metainformation about the extent of the grid (e.g `info_rho.z` and `info_rho.x` respectively return an array of the z and x positions).\n",
     "\n",
     "These two objects can then be used in a Python environnement to perform numerical analysis."
    ]