为啥 DenseFtrlValue 的实现都是空的？

[welsonzhang]

https://github.com/Qihoo360/tensornet/blob/master/core/ps/optimizer/ftrl_kernel.cc

[kiminh]

https://github.com/Qihoo360/tensornet/blob/master/core/ps/optimizer/ftrl_kernel.cc

我理解nn类模型用adagrad就行