diff --git a/examples/meta_learning.py b/examples/meta_learning.py
index 7e87b36..8ec0be5 100644
--- a/examples/meta_learning.py
+++ b/examples/meta_learning.py
@@ -181,7 +181,7 @@ def _classify_to_prototypes(
         query_targets: [N]
         return: dist: [N, M], labels: [N]
         """
-        dist = pairwise_euclidean_distance(query_feats, prototypes)  # [N, M]
+        dist = pairwise_euclidean_distance(query_feats, prototypes, True)  # [N, M]
         labels = (query_targets[:, None] == proto_labels[None, :]).float().argmax(dim=1)
         return dist, labels
 
diff --git a/examples/pre.py b/examples/pre.py
index 0abf61e..bf1ff78 100644
--- a/examples/pre.py
+++ b/examples/pre.py
@@ -30,7 +30,7 @@
 from torchmetrics.classification.auroc import AUROC
 from torchmetrics.classification.average_precision import AveragePrecision
 from torchmetrics.functional import (
-    accuracy, auroc, pairwise_cosine_similarity, pairwise_euclidean_distance
+    accuracy, auroc, pairwise_cosine_similarity
 )
 
 #
diff --git a/examples/pre_cv.py b/examples/pre_cv.py
index 102a3d1..fe67b2d 100644
--- a/examples/pre_cv.py
+++ b/examples/pre_cv.py
@@ -147,7 +147,7 @@ def load_densenet_state_dict(
 
 def NT_Xent_loss(features: Tensor, temperature: float = 0.1) -> Tuple[Tensor, Tensor, Tensor, Tensor]:
     """
-    features: Tensor[float]. [2N, E]
+    features: FloatTensor. [2N, E]
     return: loss: [], pos_idx_mean: [2N], acc: [2N], acc_5: [2N]
     """
     NINF = -torch.inf
@@ -188,3 +188,22 @@ def backward(ctx, *grads: Tensor) -> Tensor:
         res = grads[ml.get_dist_setting()[0]]
         res *= dist.get_world_size()  # for same grad with W * batch_size; mean operation in ddp across device.
         return res
+
+
+def pairwise_euclidean_distance(
+    X: Tensor,
+    Y: Tensor,
+    squared: bool = False
+) -> Tensor:
+    """
+    X: shape[N1, F]. FloatTensor
+    Y: shape[N2, F]. FloatTensor
+    return: shape[N1, N2]
+    """
+    XX = torch.einsum("ij,ij->i", X, X)
+    YY = torch.einsum("ij,ij->i", Y, Y)
+    # 
+    res = X @ Y.T
+    res.mul_(-2).add_(XX[:, None]).add_(YY)
+    res.clamp_min_(0.)
+    return res if squared else res.sqrt_()
\ No newline at end of file
diff --git a/mini_lightning/_mini_lightning.py b/mini_lightning/_mini_lightning.py
index 234e8b8..8e91ed5 100644
--- a/mini_lightning/_mini_lightning.py
+++ b/mini_lightning/_mini_lightning.py
@@ -386,7 +386,7 @@ def __init__(
         #
         self.lmodel = lmodel
         self.device_ids = device_ids
-        # 
+        #
         if deterministic is not None:
             torch.backends.cudnn.deterministic = deterministic
         deterministic = torch.backends.cudnn.deterministic
@@ -397,7 +397,7 @@ def __init__(
         torch.backends.cudnn.benchmark = benchmark
         logger.info(f"Setting deterministic: {deterministic}")
         logger.info(f"Setting benchmark: {benchmark}")
-        # 
+        #
         self.device = select_device(device_ids)
         if self.rank == -1:
             parallel_mode = "DP" if len(device_ids) > 1 else None
@@ -456,7 +456,7 @@ def __init__(
         self.model_checkpoint = model_checkpoint if model_checkpoint is not None else ModelCheckpoint()
         if self.rank in {-1, 0}:
             runs_dir = os.path.abspath(runs_dir)
-            self.version =  self._get_version(runs_dir) 
+            self.version = self._get_version(runs_dir)
             if platform.system().lower() == "windows":
                 time = dt.datetime.now().strftime("%Y-%m-%d_%H-%M-%S")  # window not support `:`
                 runs_dir = os.path.join(runs_dir, f"v{self.version}_{time}")
@@ -502,17 +502,18 @@ def _get_version(runs_dir: str) -> int:
             v_list.append(int(v))
         return max(v_list) + 1
 
-    def _check_hparams(self, hparams: Any) -> Any:
+    @classmethod
+    def _check_hparams(cls, hparams: Any) -> Any:
         if hparams is None or isinstance(hparams, (int, float, str, complex)):  # bool is a subclass of int
             return hparams
         if isinstance(hparams, Sequence):
             res = []
             for hp in hparams:
-                res.append(self._check_hparams(hp))
+                res.append(cls._check_hparams(hp))
         elif isinstance(hparams, Mapping):
             res = {}
             for k, v in hparams.items():
-                res[k] = self._check_hparams(v)
+                res[k] = cls._check_hparams(v)
         else:
             res = repr(hparams)  # e.g. function
         return res
@@ -540,7 +541,8 @@ def _metrics_update(metrics: Dict[str, MeanMetric], new_mes: Dict[str, float], p
                 continue
             metrics[k].update(v)
 
-    def _metrics_compute(self, metrics: Dict[str, MeanMetric]) -> Dict[str, float]:
+    @staticmethod
+    def _metrics_compute(metrics: Dict[str, MeanMetric]) -> Dict[str, float]:
         res = {}
         for k in metrics.keys():
             v: Tensor = metrics[k].compute()
@@ -812,7 +814,7 @@ def _train_epoch(self, dataloader: DataLoader, val_dataloader: Optional[DataLoad
                 prog_bar_mes = self._get_res_mes(_mean_metrics, _rec_mes, "prog_bar")
                 if self.rank >= 0:
                     prog_bar_mes = self._reduce_mes(prog_bar_mes, device)
-                # 
+                #
                 if self.version is not None:
                     prog_bar_mes["v"] = self.version
                 prog_bar.set_postfix(prog_bar_mes, refresh=False)  # rank > 0 disable.