[fbsync] Adding label smoothing on classification reference (#4335)

Summary:
* Adding label smoothing on classification reference.

* Replace underscore with dash.

Reviewed By: fmassa

Differential Revision: D30793326

fbshipit-source-id: f5c4faefc638e108ef6da364c7b68c59fb7aea5f

references/classification/train.py

@@ -175,7 +175,7 @@ def main(args):
     if args.distributed and args.sync_bn:
         model = torch.nn.SyncBatchNorm.convert_sync_batchnorm(model)
 
-    criterion = nn.CrossEntropyLoss()
+    criterion = nn.CrossEntropyLoss(label_smoothing=args.label_smoothing)
 
     opt_name = args.opt.lower()
     if opt_name == 'sgd':
@@ -256,6 +256,9 @@ def get_args_parser(add_help=True):
     parser.add_argument('--wd', '--weight-decay', default=1e-4, type=float,
                         metavar='W', help='weight decay (default: 1e-4)',
                         dest='weight_decay')
+    parser.add_argument('--label-smoothing', default=0.0, type=float,
+                        help='label smoothing (default: 0.0)',
+                        dest='label_smoothing')
     parser.add_argument('--lr-step-size', default=30, type=int, help='decrease lr every step-size epochs')
     parser.add_argument('--lr-gamma', default=0.1, type=float, help='decrease lr by a factor of lr-gamma')
     parser.add_argument('--print-freq', default=10, type=int, help='print frequency')