I am trying to use Lin’s Concordance Correlation Coefficient as loss function but it seems it is not work correctly as the loss value using this cost function does not change meaningfully. Can anyone help me with some advices?

Here is my code:

class ConcordanceCorCoeff(nn.Module):

```
def __init__(self):
super(ConcordanceCorCoeff, self).__init__()
self.mean = torch.mean
self.var = torch.var
self.sum = torch.sum
self.sqrt = torch.sqrt
self.std = torch.std
def forward(self, prediction, ground_truth):
mean_gt = self.mean (ground_truth, 0)
mean_pred = self.mean (prediction, 0)
var_gt = self.var (ground_truth, 0)
var_pred = self.var (prediction, 0)
v_pred = prediction - mean_pred
v_gt = ground_truth - mean_gt
cor = self.sum (v_pred * v_gt) / (self.sqrt(self.sum(v_pred ** 2)) * self.sqrt(self.sum(v_gt ** 2)))
sd_gt = self.std(ground_truth)
sd_pred = self.std(prediction)
numerator=2*cor*sd_gt*sd_pred
denominator=var_gt+var_pred+(mean_gt-mean_pred)**2
ccc = numerator/denominator
return 1-ccc
```