Model freeze capability (#679)

train.py

@@ -73,6 +73,14 @@ def train(hyp, opt, device, tb_writer=None):
     else:
         model = Model(opt.cfg, ch=3, nc=nc).to(device)  # create
 
+    # Freeze
+    freeze = ['', ]  # parameter names to freeze (full or partial)
+    if any(freeze):
+        for k, v in model.named_parameters():
+            if any(x in k for x in freeze):
+                print('freezing %s' % k)
+                v.requires_grad = False
+
     # Optimizer
     nbs = 64  # nominal batch size
     accumulate = max(round(nbs / total_batch_size), 1)  # accumulate loss before optimizing