Give a simple example of calling solve1d

lessons/python/6_functions.ipynb

@@ -440,7 +440,44 @@
     "\n",
     "Documentation systems such as [Sphinx](https://www.sphinx-doc.org/) use docstrings to produce formatted documentation.\n",
     "[NumPy](https://numpy.org/doc/1.20/docs/howto_document.html#docstrings) and [Google](https://google.github.io/styleguide/pyguide.html#s3.8.1-comments-in-doc-strings) have style guidelines for docstrings.\n",
-    "It's a good practice to pick a style and use it consistently."
+    "It's a good practice to pick a style and use it consistently.\n",
+    "\n",
+    "Before we move on, try a simple example of using `solve1d`.\n",
+    "Start by defining a variable, `z`, to diffuse."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "tags": []
+   },
+   "outputs": [],
+   "source": [
+    "z = np.zeros(5)\n",
+    "z[2] = 5\n",
+    "\n",
+    "print(z)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Now call `solve1d` to diffuse `z` for a given time step and diffusivity."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "tags": []
+   },
+   "outputs": [],
+   "source": [
+    "solve1d(z, diffusivity=0.25, time_step=0.5)\n",
+    "\n",
+    "print(z)"
    ]
   },
   {