# On the Computational Intractability of Exact and Approximate Dictionary Learning

@article{Tillmann2015OnTC, title={On the Computational Intractability of Exact and Approximate Dictionary Learning}, author={Andreas M. Tillmann}, journal={IEEE Signal Processing Letters}, year={2015}, volume={22}, pages={45-49} }

The efficient sparse coding and reconstruction of signal vectors via linear observations has received a tremendous amount of attention over the last decade. In this context, the automated learning of a suitable basis or overcomplete dictionary from training data sets of certain signal classes for use in sparse representations has turned out to be of particular importance regarding practical signal processing applications. Most popular dictionary learning algorithms involve NP-hard sparse…

## 66 Citations

### Robust Identifiability in Sparse Dictionary Learning

- Computer ScienceArXiv
- 2016

Whenever the conditions to one of the robust identifiability theorems are met, any sparsity-constrained algorithm that succeeds in approximately reconstructing the data well enough recovers the original dictionary and sparse codes up to an error commensurate with the noise.

### Learning Sparsely Used Overcomplete Dictionaries via Alternating Minimization

- Computer ScienceSIAM J. Optim.
- 2016

This paper establishes local linear convergence for this variant of alternating minimization for sparse coding and establishes that the basin of attraction for the global optimum is $\order{1/s^2}$, where $s$ is the sparsity level in each sample and the dictionary satisfies RIP.

### On the Uniqueness and Stability of Dictionaries for Sparse Representation of Noisy Signals

- Computer ScienceIEEE Transactions on Signal Processing
- 2019

This work demonstrates that some or all original dictionary elements are recoverable from noisy data even if the dictionary fails to satisfy the spark condition, its size is overestimated, or only a polynomial number of distinct sparse supports appear in the data.

### Dictionary learning with equiprobable matching pursuit

- Computer Science2017 International Joint Conference on Neural Networks (IJCNN)
- 2017

It is demonstrated via simulation experiments that dictionary learning with equiprobable selection results in higher entropy of the sparse representation and lower reconstruction and denoising errors, both in the case of ordinary matching pursuit and orthogonal matching pursuit with shift-invariant dictionaries.

### Approximate Guarantees for Dictionary Learning

- Computer ScienceCOLT
- 2019

The goal of this work is to understand what can be said in the absence of assumptions, and it is shown that the algorithmic ideas apply to a setting in which some of the columns of $X$ are outliers, thus giving similar guarantees even in this challenging setting.

### Learning fast sparsifying overcomplete dictionaries

- Computer Science2017 25th European Signal Processing Conference (EUSIPCO)
- 2017

A dictionary learning method that builds an over complete dictionary that is computationally efficient to manipulate, i.e., sparse approximation algorithms have sub-quadratic computationally complexity is proposed.

### Learning Fast Sparsifying Transforms

- Computer ScienceIEEE Transactions on Signal Processing
- 2017

This paper constructs orthogonal and nonorthogonal dictionaries that are factorized as a product of a few basic transformations and shows how the proposed transforms can balance very well data representation performance and computational complexity.

### Explorer Learning Fast Sparsifying Transforms

- Computer Science
- 2017

This paper constructs orthogonal and nonorthogonal dictionaries that are factorized as a product of a few basic transformations and shows how the proposed transforms can balance very well data representation performance and computational complexity.

### Testing Sparsity over Known and Unknown Bases

- Computer Science, MathematicsICML
- 2018

A testing algorithm which projects the input vectors to O(log p/\eps^2) dimensions and assumes that the unknown A satisfies k-restricted isometry and gives a new robust characterization of gaussian width in terms of sparsity.

### Learning Sparsely Used Overcomplete Dictionaries

- Computer ScienceCOLT
- 2014

We consider the problem of learning sparsely used overcomplete dictionaries, where each observation is a sparse combination of elements from an unknown overcomplete dictionary. We establish exact…

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