One of the oldest problems in the data stream model is to approximate the
p
-th moment
\(\Vert \mathbf {X}\Vert _p^p = \sum _{i=1}^n \mathbf {X}_i^p \)
of an underlying non-negative vector
\(\mathbf {X} \in \mathbb {R}^n \)
, which is presented as a sequence of poly(
n
) updates to its coordinates. Of particular interest is when
p
∈ (0, 2]. Although a tight space bound of
Θ
(ϵ
− 2
log
n
) bits is known for this problem when both positive and negative updates are allowed, surprisingly there is still a gap in the space complexity of this problem when all updates are positive. Specifically, the upper bound is
O
(ϵ
− 2
log
n
) bits, while the lower bound is only
Ω
(ϵ
− 2
+ log
n
) bits. Recently, an upper bound of
\(\tilde{O}(\epsilon ^{-2} + \log n) \)
bits was obtained under the assumption that the updates arrive in a
random order
.
We show that for
p
∈ (0, 1], the random order assumption is not needed. Namely, we give an upper bound for worst-case streams of
\(\tilde{O}(\epsilon ^{-2} + \log n) \)
bits for estimating
\(\Vert \mathbf {X}\Vert _p^p \)
. Our techniques also give new upper bounds for estimating the empirical entropy in a stream. On the other hand, we show that for
p
∈ (1, 2], in the natural coordinator and blackboard distributed communication topologies, there is an
\(\tilde{O}(\epsilon ^{-2}) \)
bit max-communication upper bound based on a randomized rounding scheme. Our protocols also give rise to protocols for heavy hitters and approximate matrix product. We generalize our results to arbitrary communication topologies
G
, obtaining an
\(\tilde{O}(\epsilon ^{2} \log d) \)
max-communication upper bound, where
d
is the diameter of
G
. Interestingly, our upper bound rules out natural communication complexity-based approaches for proving an
Ω
(ϵ
− 2
log
n
) bit lower bound for
p
∈ (1, 2] for streaming algorithms. In particular, any such lower bound must come from a topology with large diameter.