Fix debug stats.

egs/librispeech/ASR/pruned_transducer_stateless7/conformer.py

@@ -1342,7 +1342,7 @@ class RelPositionMultiheadAttention(nn.Module):
                 #eigs, _ = torch.symeig(attn_covar)
                 #logging.info(f"attn_weights_entropy = {attn_weights_entropy}, output_eigs = {eigs}")
 
-                attn_covar = attn_covar.mean(dim=1).sum(dim=1)  # (num_heads,)
+                attn_covar = _diag(attn_covar).mean(dim=1)  # (num_heads,)
                 embed_dim = self.in_proj2.weight.shape[1]
                 in_proj_covar = (self.in_proj2.weight.reshape(num_heads, head_dim, embed_dim) ** 2).mean(dim=(1,2))
                 out_proj_covar = (self.out_proj2.weight.reshape(embed_dim, num_heads, head_dim) ** 2).mean(dim=(0,2))