Loss functions

[pavanky]

• [x] mean squared error
• [x] mean absolute error
• [x] binary cross entropy
• [ ] negative log likelyhood

[syurkevi]

https://github.com/arrayfire/arrayfire-ml/pull/36#issuecomment-317360576 ArrayFire has lookup, however its behavior seems a bit weird, would it need to be changed in ArrayFire or just emulated in autograd?

[9prady9]

@syurkevi What kind of behavior difference are you talking about ? Can you show me an example ?