tf.contrib.tpu.cross_replica_sum( x, group_assignment=None, name=None )
Sum the input tensor across replicas according to group_assignment.
x: The local tensor to the sum.
group_assignment: Optional 2d int32 lists with shape [num_groups, num_replicas_per_group].
group_assignment[i]represents the replica ids in the ith subgroup.
name: Optional op name.
Tensor which is summed across replicas.