contrast performance evaluatation have done!

contrast/model/loss.py

@@ -0,0 +1,18 @@
+import torch
+import torch.nn as nn
+
+
+class FocalLoss(nn.Module):
+
+    def __init__(self, gamma=2):
+        super().__init__()
+        self.gamma = gamma
+        self.ce = torch.nn.CrossEntropyLoss()
+
+    def forward(self, input, target):
+
+        #print(f'theta {input.shape, input[0]}, target {target.shape, target}')
+        logp = self.ce(input, target)
+        p = torch.exp(-logp)
+        loss = (1 - p) ** self.gamma * logp
+        return loss.mean()