This reverts commit 4dc3077f96685d68b72ed67c6ecf774d44ff874f.

* update the GPU cards 

update the GPU cards ,GTX 900 series are out of date,so considering current GPU's development,add RTX 2000 series.

* GPU cost-efficiency

* Update buy-gpu.md

* Delete performance_TPU_RTX_GPUs.png

* GPU-performance

* Update buy-gpu.md

* Update buy-gpu.md

* Update buy-gpu.md

* Update buy-gpu.md

* Update buy-gpu.md

* Update buy-gpu.md

Revert "对beam search集束搜索章节的相关改写"

对beam search集束搜索章节的相关改写

修正了关于alpha的设置是惩罚长句还是短句的错误

更改束搜索beam search部分理论与描述方式

增加考虑<eos>情况序列可能空间的描述

correct deep-rnn image

Update kaggle-house-price.md

Update neural-style.md

删除无用的变量