simplify examples structure (#1247)

* simplify examples structure

* update changelog

* fix imports

* rename example

* rename scripts

* changelog

pl_examples/basic_examples/multi_node_ddp2_demo.py

@@ -0,0 +1,51 @@
+"""
+Multi-node example (GPU)
+"""
+import os
+from argparse import ArgumentParser
+
+import numpy as np
+import torch
+
+import pytorch_lightning as pl
+from pl_examples.models.lightning_template import LightningTemplateModel
+
+SEED = 2334
+torch.manual_seed(SEED)
+np.random.seed(SEED)
+
+
+def main(hparams):
+    """Main training routine specific for this project."""
+    # ------------------------
+    # 1 INIT LIGHTNING MODEL
+    # ------------------------
+    model = LightningTemplateModel(hparams)
+
+    # ------------------------
+    # 2 INIT TRAINER
+    # ------------------------
+    trainer = pl.Trainer(
+        gpus=2,
+        num_nodes=2,
+        distributed_backend='ddp2'
+    )
+
+    # ------------------------
+    # 3 START TRAINING
+    # ------------------------
+    trainer.fit(model)
+
+
+if __name__ == '__main__':
+    root_dir = os.path.dirname(os.path.realpath(__file__))
+    parent_parser = ArgumentParser(add_help=False)
+
+    # each LightningModule defines arguments relevant to it
+    parser = LightningTemplateModel.add_model_specific_args(parent_parser, root_dir)
+    hyperparams = parser.parse_args()
+
+    # ---------------------
+    # RUN TRAINING
+    # ---------------------
+    main(hyperparams)