Estimating Sparse Signals Using Integrated Wideband Dictionaries

In this paper, we introduce a wideband dictionary framework for estimating sparse signals. By formulating integrated dictionary elements spanning bands of the considered parameter space, one may efficiently find and discard large parts of the parameter space not active in the signal. After each iteration, the zero-valued parts of the dictionary may be discarded to allow a refined dictionary to be formed around the active elements, resulting in a zoomed dictionary to be used in the following iterations. Implementing this scheme allows for more accurate estimates, at a much lower computational cost, as compared to directly forming a larger dictionary spanning the whole parameter space or performing a zooming procedure using standard dictionary elements. Different from traditional dictionaries, the wideband dictionary allows for the use of dictionaries with fewer elements than the number of available samples without loss of resolution. The technique may be used on both one- and multi-dimensional signals, and may be exploited to refine several traditional sparse estimators, here illustrated with the LASSO and the SPICE estimators. Numerical examples illustrate the improved performance

Learning Sparsely Used Overcomplete Dictionaries via Alternating Minimization

We consider the problem of sparse coding, where each sample consists of a sparse linear combination of a set of dictionary atoms, and the task is to learn both the dictionary elements and the mixing coefficients. Alternating minimization is a popular heuristic for sparse coding, where the dictionary and the coefficients are estimated in alternate steps, keeping the other fixed. Typically, the coefficients are estimated via $\ell_1$ minimization, keeping the dictionary fixed, and the dictionary is estimated through least squares, keeping the coefficients fixed. In this paper, we establish local linear convergence for this variant of alternating minimization and establish that the basin of attraction for the global optimum (corresponding to the true dictionary and the coefficients) is \order{1/s^2}, where $s$ is the sparsity level in each sample and the dictionary satisfies RIP. Combined with the recent results of approximate dictionary estimation, this yields provable guarantees for exact recovery of both the dictionary elements and the coefficients, when the dictionary elements are incoherent.Comment: Local linear convergence now holds under RIP and also more general restricted eigenvalue condition

STUDENT’S ATTITUDE TOWARDS DICTIONARY AND ITS USAGE : A Case of Study for English Department Students Diponegoro University

In learning a foreign language, dictionary is one of learning aids to assist students in making decision about making sense of words in usage –in the target language. This research is conducted to discover how English Department students in Universitas Diponegoro perceive dictionary and use it to assist meaning discovery. The data in this paper is obtained from returned questionnaires previously distributed across four academic years in. The results show that dictionary is not the primary source of English vocabulary intake. Most dictionaries are bilingual (English-Indonesian or Indonesian-English), and may take the form of printed or electronic dictionary. We also discovered that the respondents tend to choose a dictionary based on the number of words listed. Further clarifications of the respondents’ answers indicate the preference of vocabulary intake, where dictionary is not a priority. Bilingual dictionaries are preferred as compared to monolingual ones with the assumption that they are easier to understand. Although the definition of word is still very loose, students seem to be more attracted to dictionaries, which claim to have vast number of entries. For practical purposes, portable dictionary or application dictionary is more preferred as they support mobility. From the results, we may conclude that dictionaries are used by the respondents with restriction in meaning discovery. We suggest that they take it to the next level, where existing linguistic features from dictionaries might also be used to assist writing

Some Thoughts on Terminology and Discipline in Design

In this speculative paper, I will argue that the design community should attempt to develop a “dictionary” of the language of design, along the same lines as the Oxford English Dictionary was and is developed: as a catalogue of the living use of terms. I will sketch an outline of how such a project could be started quite easily with modern technologies. I will then consider one word in particular – “discipline” – as an example of the need for such a dictionary, by examining the various senses of the word and how even just reflecting on that can illuminate issues of clear communications. Keywords: Terminology; Lexicography; Semantics; Dictionary; Communication; Language.</p