Add Dice loss

map2map/models/dice.py

@@ -0,0 +1,11 @@
+def dice_loss(input, target, eps=0.):
+    input = input.view(-1)
+    target = target.view(-1)
+
+    prod = (input * target).sum()
+    in_sq = (input * input).sum()
+    tgt_sq = (target * target).sum()
+
+    dice = (2 * prod + eps) / (in_sq + tgt_sq + eps)
+
+    return 1 - dice