Angular loss

[Katherinexx]

hi Mr. Hu:
I reimplement your work on mxnet, the same operation as yours in loss function. But I find that it's easy for 'dot' parameter out of range [-safe_v, safe_v], so that the loss will be the same for lots of images, and the loss will not decrease. However, without clip 'dot', the loss will be 'nan'. I change the loss to be l2 loss, the loss decrease normally.
I wonder why you set 'safe_v' parameters here, and how to avoid the 'dot' parameter out of range to make loss decrease.
Thanks a lot!

Here is my loss function:

    safe_v = 0.999999
    illum_normalized = F.L2Normalization(pred)
    _ilum_normalized = F.L2Normalization(label)
    dot = F.sum(illum_normalized*_ilum_normalized)
    dot = F.clip(dot, -safe_v, safe_v)
    angle = F.arccos(dot)*(180 / math.pi)
    mean_angle = F.mean(angle)
    return mean_angle