1,207 research outputs found
Learning Likelihoods with Conditional Normalizing Flows
Normalizing Flows (NFs) are able to model complicated distributions p(y) with
strong inter-dimensional correlations and high multimodality by transforming a
simple base density p(z) through an invertible neural network under the change
of variables formula. Such behavior is desirable in multivariate structured
prediction tasks, where handcrafted per-pixel loss-based methods inadequately
capture strong correlations between output dimensions. We present a study of
conditional normalizing flows (CNFs), a class of NFs where the base density to
output space mapping is conditioned on an input x, to model conditional
densities p(y|x). CNFs are efficient in sampling and inference, they can be
trained with a likelihood-based objective, and CNFs, being generative flows, do
not suffer from mode collapse or training instabilities. We provide an
effective method to train continuous CNFs for binary problems and in
particular, we apply these CNFs to super-resolution and vessel segmentation
tasks demonstrating competitive performance on standard benchmark datasets in
terms of likelihood and conventional metrics.Comment: 18 pages, 8 Tables, 9 Figures, Preprin
AlignFlow: Cycle Consistent Learning from Multiple Domains via Normalizing Flows
Given datasets from multiple domains, a key challenge is to efficiently
exploit these data sources for modeling a target domain. Variants of this
problem have been studied in many contexts, such as cross-domain translation
and domain adaptation. We propose AlignFlow, a generative modeling framework
that models each domain via a normalizing flow. The use of normalizing flows
allows for a) flexibility in specifying learning objectives via adversarial
training, maximum likelihood estimation, or a hybrid of the two methods; and b)
learning and exact inference of a shared representation in the latent space of
the generative model. We derive a uniform set of conditions under which
AlignFlow is marginally-consistent for the different learning objectives.
Furthermore, we show that AlignFlow guarantees exact cycle consistency in
mapping datapoints from a source domain to target and back to the source
domain. Empirically, AlignFlow outperforms relevant baselines on image-to-image
translation and unsupervised domain adaptation and can be used to
simultaneously interpolate across the various domains using the learned
representation.Comment: AAAI 202
FloWaveNet : A Generative Flow for Raw Audio
Most modern text-to-speech architectures use a WaveNet vocoder for
synthesizing high-fidelity waveform audio, but there have been limitations,
such as high inference time, in its practical application due to its ancestral
sampling scheme. The recently suggested Parallel WaveNet and ClariNet have
achieved real-time audio synthesis capability by incorporating inverse
autoregressive flow for parallel sampling. However, these approaches require a
two-stage training pipeline with a well-trained teacher network and can only
produce natural sound by using probability distillation along with auxiliary
loss terms. We propose FloWaveNet, a flow-based generative model for raw audio
synthesis. FloWaveNet requires only a single-stage training procedure and a
single maximum likelihood loss, without any additional auxiliary terms, and it
is inherently parallel due to the characteristics of generative flow. The model
can efficiently sample raw audio in real-time, with clarity comparable to
previous two-stage parallel models. The code and samples for all models,
including our FloWaveNet, are publicly available.Comment: 9 pages, ICML'201
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