Questions tagged [wavelet]

A wavelet denotes a wave-like, generally localized, oscillating function, equipped with certain relationships across scales. A wavelet transformation describes a representation of data, decomposed onto a set of different wavelet functions, often forming a basis or a frame.

Wavelets can be informally described as localised, oscillatory functions designed to possess attractive properties that Fourier-related functions (sines, cosines) do not enjoy. They are generated by dilation, translation, rotation of a reduced set of functions. Their discretization yields sets of vectors forming bases or frames. Their design permits the decomposition of data at different scales or resolutions, with some attractive features for time-series statistical analysis, e.g. sparse representations, separation of polynomial trends, change detection, decorrelation, noise whitening. They have been used for nonparametric regression, in conjunction with efficient estimation techniques, notably the Stein's Unbiased Risk Estimator (SURE) procedure.

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Application of wavelets to time-series-based anomaly detection algorithms

I've been beginning to work my way through Statistical Data Mining Tutorials by Andrew Moore (highly recommended for anyone else first venturing into this field). I started by reading this extremely interesting PDF entitled "Introductory overview…
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Wavelet-domain Gaussian processes: what is the covariance?

I've been reading Maraun et al, "Nonstationary Gaussian processes in wavelet domain: Synthesis, estimation, and significant testing" (2007) which defines a class of non-stationary GPs that can be specified by multipliers in wavelet domain. A…
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What is the difference between functional data analysis and high dimensional data analysis

There are a lot of references in the statistic literature to "functional data" (i.e. data that are curves), and in parallel, to "high dimensional data" (i.e. when data are high dimensional vectors). My question is about the difference between the…
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Boundary effect in a wavelet multi resolution analysis

What are the methods to minimize the effect of boundaries in a wavelet decomposition? I use R and the package waveslim. I have found for instance the function ?brick.wall but I am not too use how to use it. I am not sure the best solution is to…
RockScience
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time series dimensionality reduction

I have a call center data (such as one below) that has call data collected every 15 minutes. For a day the periodicity is 96 and for a week the periodicity is (7 x 96 = 672). If I would like to forecast this data I can use models that handle…
forecaster
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How to denoise a "Poissonous" time series

I have $N$ time series each of which can be modeled as $$y_{kt}=Ax_{kt}+b+\varepsilon_{kt}\quad(1\le k\le N,1\le t\le T),$$ where $x_{kt}\sim\text{Pois}(\lambda\Delta t)$ and $\varepsilon_{kt}\sim N(0,\sigma^2)$. Parameters $A$, $b$ and $\sigma^2$…
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Finding the instantaneous period of a signal (or calculating period degradation)

I have a signal, of varying amplitude, and after a certain point in time, I expect to see the period of this signal lengthen. I am looking for a way to measure the lengthening of this period. Is this a way I can calculate the instantaneous period of…
Ina
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Wavelet analysis, scaling filter: where does the square root of 2 go to?

In their great book "Wavelet methods for time series analysis" (2006), Percival & Walden state on p. 83 that the first-round pyramid algorithm scaling filter coefficients $\tilde{V}_{i,t}$ can be approximated by $\frac{1}{N}…
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Wavelet smoothing at different scales

I would like to perform wavelet smoothing at different scales in R. I got the idea from this figure (panel A) were they measure the density/intensity of a particular signal at different scales. Here the image shows the linear coordinates along one…
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time-series analysis Vs statistical signal processing

Is there a way to identify when to use time series analysis or signal processing. Time series data analysis can be divided to signal processing and normal time series analysis. In signal processing the data is analysed in frequency or time domain.…
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Compressing data using wavelets with R

I'm trying to compress data using wavelets and I wanted to do it with R. Could anyone tell me if there is such a tool? Thanks in advance.
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Finding similarities using Wavelet transform

I have a time serie and I want to find similarities in it. For the first step I have calculated Haar-wavelet coefficients for this time serie, and now I don't know exactly how should I continue should I extract features from this transformed data,…
TangoStar
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Detrending & cross-correlation function

I am looking for some help with my time-series data. What is the best method of detrending/transformation of these two variables, so I do not violate assumptions of stationarity when applying a cross correlation function (to find out if one series…
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Why does the residual 1x1 conv in wavenet not have an activation?

I have been trying to implement a wavenet. From the papers and designs I have looked at on github I have come up with the following... for i, (last, d) in enumerate(is_last([1, 2, 4, 8, 16, 32, 64, 128, 256] * 4)): h = layers.Conv1D(64, 2,…
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Unbalanced Haar Wavelets and R package unbalhaar

I have found the article by Fryzlewicz (2007) and his R package unbalhaar. I do not understand well the outputs of his functions and in particular of the best.unbal.haar.bu() function. Here is the documentation of it : best.unbal.haar.bu. From his…
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