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Update to use log_sigmoid in FocalLoss #7534

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Merged
KumoLiu merged 3 commits into from
Mar 18, 2024
Merged

Update to use log_sigmoid in FocalLoss #7534

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a9a2d3a
fix #7533
KumoLiu Mar 12, 2024
9e22a55
fix flake8
KumoLiu Mar 12, 2024
da2d152
Merge branch 'dev' into focal-loss
KumoLiu Mar 18, 2024
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5 changes: 2 additions & 3 deletions monai/losses/focal_loss.py
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Expand Up @@ -234,9 +234,8 @@ def sigmoid_focal_loss(
"""
# computing binary cross entropy with logits
# equivalent to F.binary_cross_entropy_with_logits(input, target, reduction='none')
# see also https://github.com/pytorch/pytorch/blob/v1.9.0/aten/src/ATen/native/Loss.cpp#L231
max_val = (-input).clamp(min=0)
loss: torch.Tensor = input - input * target + max_val + ((-max_val).exp() + (-input - max_val).exp()).log()
# see also https://github.com/pytorch/pytorch/blob/main/aten/src/ATen/native/Loss.cpp#L363
loss: torch.Tensor = input - input * target - F.logsigmoid(input)

# sigmoid(-i) if t==1; sigmoid(i) if t==0 <=>
# 1-sigmoid(i) if t==1; sigmoid(i) if t==0 <=>
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2 changes: 1 addition & 1 deletion tests/test_focal_loss.py
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Expand Up @@ -132,7 +132,7 @@ def test_consistency_with_cross_entropy_2d_no_reduction(self):
error = np.abs(a - b)
max_error = np.maximum(error, max_error)

assert np.allclose(max_error, 0)
assert np.allclose(max_error, 0, atol=1e-6)

def test_consistency_with_cross_entropy_2d_onehot_label(self):
"""For gamma=0 the focal loss reduces to the cross entropy loss"""
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