Multiphase doc

docs/GetStarted.md

@@ -97,3 +97,4 @@ The experiment has been running now, NNI provides WebUI for you to view experime
 * [How to run an experiment on local (with multiple GPUs)?](tutorial_1_CR_exp_local_api.md)
 * [How to run an experiment on multiple machines?](tutorial_2_RemoteMachineMode.md)
 * [How to run an experiment on OpenPAI?](PAIMode.md)
+* [How to create a multi-phase experiment](multiPhase.md)

docs/multiPhase.md

@@ -0,0 +1,31 @@
+**Create multi-phase experiment**
+
+Multi-phase experiments refer to experiments whose trial jobs request multiple hyper parameters from tuner and report multiple final results to NNI.
+To use multi-phase experiment, the Tuner needs to be a subclass of nni.multi_phase.MultiPhaseTuner. For example, this [ENAS tuner](https://github.com/countif/enas_nni/blob/master/nni/examples/tuners/enas/src/nni_controller.py) is a multi-phase Tuner.
+```multiPhase``` field needs to be set to ```true``` in configuration file, for example:
+
+```yml
+...
+multiPhase: true
+tuner:
+  codeDir: tuners/enas
+  classFileName: nni_controller_ptb.py
+  className: ENASTuner
+  classArgs:
+    say_hello: "hello"
+...
+```
+
+
+Then, nni.get_next_parameter() API can be invoked for multiple times in a trial, for example:
+
+```python
+for i in range(5):
+    # get parameters form tuner
+    hyper_params = nni.get_next_parameter()
+
+    # consume the params
+    # ...
+```
+
+API ```nni.report_final_result()``` can be called one time for each hyper parameters.