keras 中如何自定义损失函数？
http://lazycoderx.com/2016/10/09/keras%E4%BF%9D%E5%AD%98%E6%A8%A1%E5%9E%8B%E6%97%B6%E4%BD%BF%E7%94%A8%E8%87%AA%E5%AE%9A%E4%B9%89%E6%8D%9F%E5%A4%B1%E5%87%BD%E6%95%B0/
http://www.voidcn.com/blog/zjm750617105/article/p-5954719.html
http://lazycoderx.com/2016/10/09/keras%E4%BF%9D%E5%AD%98%E6%A8%A1%E5%9E%8B%E6%97%B6%E4%BD%BF%E7%94%A8%E8%87%AA%E5%AE%9A%E4%B9%89%E6%8D%9F%E5%A4%B1%E5%87%BD%E6%95%B0/
http://www.voidcn.com/blog/zjm750617105/article/p-5954719.html