Enable AdamW optimizer (#6152)

train.py

@@ -22,7 +22,7 @@
 import yaml
 from torch.cuda import amp
 from torch.nn.parallel import DistributedDataParallel as DDP
-from torch.optim import SGD, Adam, lr_scheduler
+from torch.optim import SGD, Adam, AdamW, lr_scheduler
 from tqdm import tqdm
 
 FILE = Path(__file__).resolve()
@@ -155,8 +155,10 @@ def train(hyp,  # path/to/hyp.yaml or hyp dictionary
         elif hasattr(v, 'weight') and isinstance(v.weight, nn.Parameter):  # weight (with decay)
             g1.append(v.weight)
 
-    if opt.adam:
+    if opt.optimizer == 'Adam':
         optimizer = Adam(g0, lr=hyp['lr0'], betas=(hyp['momentum'], 0.999))  # adjust beta1 to momentum
+    elif opt.optimizer == 'AdamW':
+        optimizer = AdamW(g0, lr=hyp['lr0'], betas=(hyp['momentum'], 0.999))  # adjust beta1 to momentum
     else:
         optimizer = SGD(g0, lr=hyp['lr0'], momentum=hyp['momentum'], nesterov=True)
 
@@ -460,7 +462,7 @@ def parse_opt(known=False):
     parser.add_argument('--device', default='', help='cuda device, i.e. 0 or 0,1,2,3 or cpu')
     parser.add_argument('--multi-scale', action='store_true', help='vary img-size +/- 50%%')
     parser.add_argument('--single-cls', action='store_true', help='train multi-class data as single-class')
-    parser.add_argument('--adam', action='store_true', help='use torch.optim.Adam() optimizer')
+    parser.add_argument('--optimizer', type=str, choices=['SGD', 'Adam', 'AdamW'], default='SGD', help='optimizer')
     parser.add_argument('--sync-bn', action='store_true', help='use SyncBatchNorm, only available in DDP mode')
     parser.add_argument('--workers', type=int, default=8, help='max dataloader workers (per RANK in DDP mode)')
     parser.add_argument('--project', default=ROOT / 'runs/train', help='save to project/name')