在theano扫描中执行更新

Question

rng = RandomStreams()

res, updates = th.map(lambda x: rng.binomial(), 
                      T.arange(10))

final_res, final_updates = th.scan(lambda x: res, 
                                   sequences=T.arange(10))

想象一下，我想要实现一些类似的东西。问题是map使用RNG，所以它有自己的非空白更新来更新RNG状态。如何强制updates在scan内执行？

Answer 1

根据scan源代码文档： The function is expected to return two things. One is a list of outputs ordered in the same order as ``outputs_info``, with the difference that there should be only one output variable per output initial state (even if no tap value is used). Secondly `fn` should return an update dictionary (that tells how to update any shared variable after each iteration step). The dictionary can optionally be given as a list of tuples. There is no constraint on the order of these two list, ``fn`` can return either ``(outputs_list, update_dictionary)`` or ``(update_dictionary, outputs_list)`` or just one of the two (in case the other is empty).