[RTDETR]Fix val loss (#3280)

ultralytics/nn/modules/head.py

@@ -158,6 +158,7 @@ class Classify(nn.Module):
 
 
 class RTDETRDecoder(nn.Module):
+    export = False  # export mode
 
     def __init__(
             self,
@@ -246,9 +247,12 @@ class RTDETRDecoder(nn.Module):
                                               self.dec_score_head,
                                               self.query_pos_head,
                                               attn_mask=attn_mask)
-        if not self.training:
-            dec_scores = dec_scores.sigmoid_()
-        return dec_bboxes, dec_scores, enc_bboxes, enc_scores, dn_meta
+        x = dec_bboxes, dec_scores, enc_bboxes, enc_scores, dn_meta
+        if self.training:
+            return x
+        # (bs, 300, 4+nc)
+        y = torch.cat((dec_bboxes.squeeze(0), dec_scores.squeeze(0).sigmoid()), -1)
+        return y if self.export else (y, x)
 
     def _generate_anchors(self, shapes, grid_size=0.05, dtype=torch.float32, device='cpu', eps=1e-2):
         anchors = []