diff --git a/wwf/vision/object_detection/metrics.py b/wwf/vision/object_detection/metrics.py
index 24ac09b4..a1cf14b9 100644
--- a/wwf/vision/object_detection/metrics.py
+++ b/wwf/vision/object_detection/metrics.py
@@ -17,8 +17,8 @@ def activ_to_bbox(acts, anchors, flatten=True):
 def bbox_to_activ(bboxes, anchors, flatten=True):
     "Return the target of the model on `anchors` for the `bboxes`."
     if flatten:
-        t_centers = (bboxes[...,:2] - anchors[...,:2]) / anchors[...,2:] 
-        t_sizes = torch.log(bboxes[...,2:] / anchors[...,2:] + 1e-8) 
+        t_centers = (bboxes[...,:2] - anchors[...,:2]) / anchors[...,2:]
+        t_sizes = torch.log(bboxes[...,2:] / anchors[...,2:] + 1e-8)
         return torch.cat([t_centers, t_sizes], -1).div_(bboxes.new_tensor([[0.1, 0.1, 0.2, 0.2]]))
     else: return [activ_to_bbox(act,anc) for act,anc in zip(acts, anchors)]
     return res
@@ -26,7 +26,11 @@ def bbox_to_activ(bboxes, anchors, flatten=True):
 def encode_class(idxs, n_classes):
     target = idxs.new_zeros(len(idxs), n_classes).float()
     mask = idxs != 0
-    i1s = LongTensor(list(range(len(idxs))))
+    if cuda.is_available():
+        tensor_fn = torch.cuda.LongTensor
+    else:
+        tensor_fn = LongTensor
+    i1s = tensor_fn(list(range(len(idxs))))
     target[i1s[mask],idxs[mask]-1] = 1
     return target
 
@@ -83,7 +87,7 @@ def intersection(anchors, targets):
     ancs, tgts = ancs.unsqueeze(1).expand(a,t,4), tgts.unsqueeze(0).expand(a,t,4)
     top_left_i = torch.max(ancs[...,:2], tgts[...,:2])
     bot_right_i = torch.min(ancs[...,2:], tgts[...,2:])
-    sizes = torch.clamp(bot_right_i - top_left_i, min=0) 
+    sizes = torch.clamp(bot_right_i - top_left_i, min=0)
     return sizes[...,0] * sizes[...,1]
 
 def IoU_values(anchs, targs):
@@ -99,21 +103,21 @@ def __init__(self, gamma:float=2., alpha:float=0.25,  pad_idx:int=0, scales=None
         self.gamma,self.alpha,self.pad_idx,self.reg_loss = gamma,alpha,pad_idx,reg_loss
         self.scales = ifnone(scales, [1,2**(-1/3), 2**(-2/3)])
         self.ratios = ifnone(ratios, [1/2,1,2])
-        
+
     def _change_anchors(self, sizes) -> bool:
         if not hasattr(self, 'sizes'): return True
         for sz1, sz2 in zip(self.sizes, sizes):
             if sz1[0] != sz2[0] or sz1[1] != sz2[1]: return True
         return False
-    
+
     def _create_anchors(self, sizes, device:torch.device):
         self.sizes = sizes
         self.anchors = create_anchors(sizes, self.ratios, self.scales).to(device)
-    
+
     def _unpad(self, bbox_tgt, clas_tgt):
         i = torch.min(torch.nonzero(clas_tgt-self.pad_idx))
         return tlbr2cthw(bbox_tgt[i:]), clas_tgt[i:]-1+self.pad_idx
-    
+
     def _focal_loss(self, clas_pred, clas_tgt):
         encoded_tgt = encode_class(clas_tgt, clas_pred.size(1))
         ps = torch.sigmoid(clas_pred.detach())
@@ -122,7 +126,7 @@ def _focal_loss(self, clas_pred, clas_tgt):
         weights.pow_(self.gamma).mul_(alphas)
         clas_loss = F.binary_cross_entropy_with_logits(clas_pred, encoded_tgt, weights, reduction='sum')
         return clas_loss
-        
+
     def _one_loss(self, clas_pred, bbox_pred, clas_tgt, bbox_tgt):
         bbox_tgt, clas_tgt = self._unpad(bbox_tgt, clas_tgt)
         matches = match_anchors(self.anchors, bbox_tgt)
@@ -139,7 +143,7 @@ def _one_loss(self, clas_pred, bbox_pred, clas_tgt, bbox_tgt):
         clas_tgt = torch.cat([clas_tgt.new_zeros(1).long(), clas_tgt])
         clas_tgt = clas_tgt[matches[clas_mask]]
         return bb_loss + self._focal_loss(clas_pred, clas_tgt)/torch.clamp(bbox_mask.sum(), min=1.)
-    
+
     def forward(self, output, bbox_tgts, clas_tgts):
         clas_preds, bbox_preds, sizes = output
         if self._change_anchors(sizes): self._create_anchors(sizes, clas_preds.device)