add tensorboard doc (#263)

docs/index.rst

@@ -58,9 +58,10 @@ Abstractions
     :maxdepth: 1
     :caption: Tutorial
 
-    getting_started.rst
-    new_alg.rst
-    save_param.rst
+    tutorial/getting_started.rst
+    tutorial/new_alg.rst
+    tutorial/save_param.rst
+    tutorial/tensorboard.rst
 
 .. toctree::
     :maxdepth: 2

docs/tutorial/tensorboard.rst

+Tensorboard
+===============
+
+Visualize the results with tensorboard.
+
+add_scalar
+-------------
+
+Common used arguments:
+
+* tensorboard.add_scalar(tag, scalar_value, global_step=None)
+    * tag *(string)* – Data identifier
+    * scalar_value *(float or string/blobname)* – Value to save
+    * global_step *(int)* – Global step value to record
+
+Example:
+
+.. code-block:: python
+
+    from parl.utils import tensorboard
+
+    x = range(100)
+    for i in x:
+        tensorboard.add_scalar('y=2x', i * 2, i)
+
+Expected result:
+
+    .. image:: add_scalar.jpg
+        :scale: 50 %
+            
+add_histogram
+----------------
+
+Common used arguments:
+
+* tensorboard.add_scalar(tag, scalar_value, global_step=None)
+    * tag *(string)* – Data identifier
+    * values *(torch.Tensor, numpy.array, or string/blobname)* – Values to build histogram
+    * global_step *(int)* – Global step value to record
+
+Example:
+
+.. code-block:: python
+
+    from parl.utils import tensorboard
+    import numpy as np
+
+    for i in range(10):
+        x = np.random.random(1000)
+        tensorboard.add_histogram('distribution centers', x + i, i)
+
+Expected result:
+
+    .. image:: add_histogram.jpg
+        :scale: 50 %