Merge pull request #47 from dseuss/feat-docs

Add images to example notebook

examples/mpnum_intro.ipynb

@@ -129,8 +129,11 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Because the MPA has one physical leg per site, we have created a matrix product *state* (i.e. a tensor train). \n",
+    "Because the MPA has one physical leg per site, we have created a matrix product *state* (i.e. a tensor train). In the [graphical notation](http://mpnum.readthedocs.io/en/latest/intro.html#graphical-notation), this MPS looks like this\n",
     "\n",
+    "![](http://mpnum.readthedocs.io/en/latest/_images/tensors_mps_no_names.png)\n",
+    "\n",
+    "Note that `mpnum` internally stores the local tensors of the matrix product representation on the right hand side. We see below how to obtain the \"dense\" tensor from an `MPArray`.\n",
     "Dimension of each physical leg:"
    ]
   },
@@ -585,7 +588,11 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Basic properties:"
+    "In graphical notation, `mpo` looks like this\n",
+    "\n",
+    "![](http://mpnum.readthedocs.io/en/latest/_images/notebook_mpo.png)\n",
+    "\n",
+    "It's basic properties are:"
    ]
   },
   {
@@ -853,7 +860,11 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "The result is a new MPS, with local dimension changed by ``mpo``.  The ``axes`` argument is optional and defaults to ``axes=(-1, 0)`` -- i.e. contracting, at each site, the last pyhsical index of the first factor with the first physical index of the second factor. More specifically, the ``axes`` argument  specifies which _physical legs_ should be contracted:  ``axes[0]`` specifies the physical in the first argument, and ``axes[1]`` specifies the physical leg in the second argument.  This means that the same product can be achieved with"
+    "The result is a new MPS, with local dimension changed by ``mpo`` and looks like this:\n",
+    "\n",
+    "![](http://mpnum.readthedocs.io/en/latest/_images/notebook_mpo_mps.png)\n",
+    "\n",
+    "The ``axes`` argument is optional and defaults to ``axes=(-1, 0)`` -- i.e. contracting, at each site, the last pyhsical index of the first factor with the first physical index of the second factor. More specifically, the ``axes`` argument  specifies which _physical legs_ should be contracted:  ``axes[0]`` specifies the physical in the first argument, and ``axes[1]`` specifies the physical leg in the second argument.  This means that the same product can be achieved with"
    ]
   },
   {