解决方案1:
cross_entropy = -tf.reduce_sum(y_*tf.log(tf.clip_by_value(y_conv,1e-10,1.0)))
解决方案2:(推荐)
cross_entropy = -tf.reduce_sum(y_*tf.log(y_conv + 1e-10))
原文参考:http://stackoverflow.com/questions/33712178/tensorflow-nan-bug
解释参考:http://blog.youkuaiyun.com/sinat_16823063/article/details/53699849