Merge pull request #570 from KevinMusgrave/dev

v1.7.0

.flake8

@@ -1,12 +1,18 @@
 [flake8]
 
 extend-ignore =
-    E266 # too many leading '#' for block comment
-    E203 # whitespace before ':'
-    E402 # module level import not at top of file
-    E501 # line too long
-    E741 # ambiguous variable names
-    E265 # block comment should start with #
+    # too many leading '#' for block comment
+    E266 
+    # whitespace before ':'
+    E203 
+    # module level import not at top of file
+    E402 
+    # line too long
+    E501 
+    # ambiguous variable names
+    E741 
+    # block comment should start with #
+    E265 
 
 per-file-ignores =
     __init__.py:F401

src/pytorch_metric_learning/__init__.py

@@ -1 +1 @@
-__version__ = "1.6.3"
+__version__ = "1.7.0"

src/pytorch_metric_learning/losses/arcface_loss.py

@@ -21,7 +21,19 @@ def cast_types(self, dtype, device):
 
     def modify_cosine_of_target_classes(self, cosine_of_target_classes):
         angles = self.get_angles(cosine_of_target_classes)
-        return torch.cos(angles + self.margin)
+
+        # Compute cos of (theta + margin) and cos of theta
+        cos_theta_plus_margin = torch.cos(angles + self.margin)
+        cos_theta = torch.cos(angles)
+
+        # Keep the cost function monotonically decreasing
+        unscaled_logits = torch.where(
+            angles <= np.deg2rad(180) - self.margin,
+            cos_theta_plus_margin,
+            cos_theta - self.margin * np.sin(self.margin),
+        )
+
+        return unscaled_logits
 
     def scale_logits(self, logits, *_):
         return logits * self.scale

tests/losses/test_arcface_loss.py

@@ -36,9 +36,16 @@ def test_arcface_loss(self):
 
             for i, c in enumerate(labels):
                 acos = torch.acos(torch.clamp(logits[i, c], -1, 1))
-                logits[i, c] = torch.cos(
-                    acos + torch.tensor(np.radians(margin), dtype=dtype).to(TEST_DEVICE)
-                )
+                if acos <= (np.pi - np.radians(margin)):
+                    logits[i, c] = torch.cos(
+                        acos
+                        + torch.tensor(np.radians(margin), dtype=dtype).to(TEST_DEVICE)
+                    )
+                else:
+                    mg = np.radians(margin)
+                    logits[i, c] -= torch.tensor(mg * np.sin(mg), dtype=dtype).to(
+                        TEST_DEVICE
+                    )
 
             correct_loss = F.cross_entropy(logits * scale, labels.to(TEST_DEVICE))