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Learning mixtures of product distributions over discrete domains
We consider the problem of learning mixtures of product distributions over discrete domains in the distribution learning framework introduced by Kearns et al. [18]. We give a poly(n/ε) time algorithm for learning a mixture of k arbitrary product distributions over the n-dimensional Boolean cube {0,1}n to accuracy ε, for any constant k. Previous polynomial time algorithms could only achieve this for k = 2 product distributions; our result answers an open question stated independently in [8] and [14]. We further give evidence that no polynomial time algorithm can succeed when k is superconstant, by reduction from a notorious open problem in PAC learning. Finally, we generalize our poly(n/ε) time algorithm to learn any mixture of k = O(1) product distributions over {0, 1, . . . , b}n, for any b = O(1)
Learning mixtures of structured distributions over discrete domains
Let be a class of probability distributions over the discrete
domain We show that if satisfies a rather
general condition -- essentially, that each distribution in can
be well-approximated by a variable-width histogram with few bins -- then there
is a highly efficient (both in terms of running time and sample complexity)
algorithm that can learn any mixture of unknown distributions from
We analyze several natural types of distributions over , including
log-concave, monotone hazard rate and unimodal distributions, and show that
they have the required structural property of being well-approximated by a
histogram with few bins. Applying our general algorithm, we obtain
near-optimally efficient algorithms for all these mixture learning problems.Comment: preliminary full version of soda'13 pape
Bayesian Learning of Sum-Product Networks
Sum-product networks (SPNs) are flexible density estimators and have received
significant attention due to their attractive inference properties. While
parameter learning in SPNs is well developed, structure learning leaves
something to be desired: Even though there is a plethora of SPN structure
learners, most of them are somewhat ad-hoc and based on intuition rather than a
clear learning principle. In this paper, we introduce a well-principled
Bayesian framework for SPN structure learning. First, we decompose the problem
into i) laying out a computational graph, and ii) learning the so-called scope
function over the graph. The first is rather unproblematic and akin to neural
network architecture validation. The second represents the effective structure
of the SPN and needs to respect the usual structural constraints in SPN, i.e.
completeness and decomposability. While representing and learning the scope
function is somewhat involved in general, in this paper, we propose a natural
parametrisation for an important and widely used special case of SPNs. These
structural parameters are incorporated into a Bayesian model, such that
simultaneous structure and parameter learning is cast into monolithic Bayesian
posterior inference. In various experiments, our Bayesian SPNs often improve
test likelihoods over greedy SPN learners. Further, since the Bayesian
framework protects against overfitting, we can evaluate hyper-parameters
directly on the Bayesian model score, waiving the need for a separate
validation set, which is especially beneficial in low data regimes. Bayesian
SPNs can be applied to heterogeneous domains and can easily be extended to
nonparametric formulations. Moreover, our Bayesian approach is the first, which
consistently and robustly learns SPN structures under missing data.Comment: NeurIPS 2019; See conference page for supplemen
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