fix a little bug about resume (#1628)

* fix a little bug about resume

When resuming, we need to start from the last epoch not 0.

* the second way for resuming

the second way for resuming

references/detection/train.py

@@ -114,6 +114,7 @@ def main(args):
         model_without_ddp.load_state_dict(checkpoint['model'])
         optimizer.load_state_dict(checkpoint['optimizer'])
         lr_scheduler.load_state_dict(checkpoint['lr_scheduler'])
+        args.start_epoch = checkpoint['epoch'] + 1
         
     if args.test_only:
         evaluate(model, data_loader_test, device=device)
@@ -121,7 +122,7 @@ def main(args):
 
     print("Start training")
     start_time = time.time()
-    for epoch in range(args.epochs):
+    for epoch in range(args.start_epoch, args.epochs):
         if args.distributed:
             train_sampler.set_epoch(epoch)
         train_one_epoch(model, optimizer, data_loader, device, epoch, args.print_freq)
@@ -131,7 +132,8 @@ def main(args):
                 'model': model_without_ddp.state_dict(),
                 'optimizer': optimizer.state_dict(),
                 'lr_scheduler': lr_scheduler.state_dict(),
-                'args': args},
+                'args': args,
+                'epoch': epoch},
                 os.path.join(args.output_dir, 'model_{}.pth'.format(epoch)))
 
         # evaluate after every epoch
@@ -171,6 +173,7 @@ if __name__ == "__main__":
     parser.add_argument('--print-freq', default=20, type=int, help='print frequency')
     parser.add_argument('--output-dir', default='.', help='path where to save')
     parser.add_argument('--resume', default='', help='resume from checkpoint')
+    parser.add_argument('--start_epoch', default=0, type=int, help='start epoch')
     parser.add_argument('--aspect-ratio-group-factor', default=3, type=int)
     parser.add_argument(
         "--test-only",