Segmentation support & other enchancements (#40)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/yolo/utils/torch_utils.py

@@ -179,3 +179,13 @@ def smart_inference_mode(torch_1_9=check_version(torch.__version__, '1.9.0')):
 def intersect_state_dicts(da, db, exclude=()):
     # Dictionary intersection of matching keys and shapes, omitting 'exclude' keys, using da values
     return {k: v for k, v in da.items() if k in db and all(x not in k for x in exclude) and v.shape == db[k].shape}
+
+
+def is_parallel(model):
+    # Returns True if model is of type DP or DDP
+    return type(model) in (nn.parallel.DataParallel, nn.parallel.DistributedDataParallel)
+
+
+def de_parallel(model):
+    # De-parallelize a model: returns single-GPU model if model is of type DP or DDP
+    return model.module if is_parallel(model) else model