Found two flaws in ArcMarginHeader

[alexkrz]

Hi,

I stumbled across your repository to compare different approaches for computing face embeddings. I like your approach to construct the ArcMarginHeader class as base class for all other approaches. However, when training a model with the ArcFaceHeader, I noticed two flaws in your ArcMarginHeader class.

Both flaws appear in the forward() function:

1. line 28:

   self.linear.weight = torch.nn.Parameter(self.normalize(self.linear.weight))

   You need to initialize the weight parameter when initializing the header class instead of initiliazing it again in every forward pass.

2. line 32:

   theta = torch.acos(logits).clamp(-1, 1)

   The arccos must not be clamped to (-1, 1), as the returned function values are between 0 and pi.

I will create a PR that fixes both issues.