# Questions tagged [wavelet]

Referring to the study of brief oscillations whose amplitude grows and decays in a finite time.

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### Can the Runge-Kuta algorithm help in reducing numerical dispersion and anisotropy when using the FDM to solve the 2D wave equation? [closed]

I am currently studying the effects of group velocity on the finite difference solution of the wave equation. Most of what I learned is from this source. I understand that high frequency components in ...
34 views

### Doubt of wavelets about the return of comand plot() of package Wavethresh in R language

I take a plot of father wavelet with this code library(wavethresh) y <- c(1,1,7,9,2,8,8,6) ywd <- wd(y, filter.number=1, family='DaubExPhase') plot(ywd) But ...
51 views

### Dimensionality reduction between discrete wavelet families

I have what it may be a ridiculous question (since I don't know much about wavelets), but here I go. I am using different Discrete Wavelet families to extract texture features from images. I plan to ...
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### Numerical evaluation of Fourier transform of a scaling function

Given a set of filter taps $\{h_n\}_{n=0}^{m-1}$, define a scaling function $\phi$ by $$\phi(x) = \sqrt{2}\sum_{n} h_n \phi(2x-n).$$ In keeping with the notation from Daubechies "Ten Lectures on ...
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### Wrong Boundary Conditions Result Using Wavelet Collocation

I have a functional $S$, $$S = \int_{x_0}^{x_b} dx \frac{1}{z(x)^d} \sqrt{1 + \frac{z'(x)^2}{f(z)}}, \qquad f(z) = 1-\left(\frac{z(x)}{z_h}\right)^{d+1}$$ where $d=3$ is the dimension and $z_h$ is ...
• 163
1 vote
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### Questions on Daubechies wavelets

Is the refinement equation for the orthonormal Daubechies scaling function $$\phi(x) = \sqrt{2} \sum_n h_n \phi(2x-n) \;?$$ The filter coefficients for Daubechies wavelets have been given e.g. in this ...
• 331
1 vote
87 views

### Advantage of fractional Fourier transform over multiscale wavelet?

What could be the arguments of using fractional Fourier transform instead of multiscale wavelet for data analysis ? Optimization of the good time-frequency domain parameter? good in the sens of best ...
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39 views

### Open Source Packages Implementing Continuous Wavelet and Scaling Functions

I'm looking for an open source software package that provides a fast evaluation of continuous Daubechies/Symmlet wavelet/scaling functions. GSL only has the discrete wavelets, and PyWavelets comes ...
• 2,155
1 vote
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### How to construct Diffusion Wavelet Packets?

I understand the idea of constructing Low-pass and High-pass filters as a projection on the Numerical Range and Numerical Kernel of dyadic powers of a diffusion operator in the work Diffusion Wavelet ...
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### Can Mallat's pyramidal algorithm be extended to non-power of 2 input sizes?

Mallat's pyramidal algorithm for the discrete wavelet transform operates on power-of-2 vector lengths. Can it be extended to work on inputs of any size without resorting to zero padding?
• 2,155
1 vote
341 views

### What is the difference between the curl component, and the divergence-free component, of a vector field?

The term divergence-free sounds more general and appears particularly in wavelet-related approaches to the Navier-Stokes equations. However I have yet to find a discussion focusing on the distinction, ...
• 209
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### Reduction of linear system with decaying unknown

I have a linear system of equations $Ax = b$ where the number of unknowns $N$ is intractably large but the right-hand side has only small support and the unknown $x$ is known to decay exponentially. I ...
• 445
1 vote
111 views

### Adjoint of the MATLAB $\tt dwt3$ (3D wavelet transform) operator

How do I compute the adjoint of MATLAB's dwt3 operator? In other words, how do I compute the adjoint of the linear operator that takes a 3D complex array ...
• 181
1 vote
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### Computing 3-term Connection Coefficients for Wavelets

I am trying to calculate the three-term connection coefficients $$Λ_{l,m}^{d_1,d_2,d_3} = ∫_{-∞}^∞ φ^{(d_1)}(x) φ^{(d_2)}_l(x) φ^{(d_3)}_m(x) dx$$ for Daubechies wavelets numerically using Python. ...
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1 vote
415 views

### How to add a Ricker Wavelet (Mexican Hat) to a 2D/ 3D fem mesh?

I have a 2D square mesh and a 3D beam shaped mesh and I want to propagate a seismic wave in them. I am trying to simulate them using Open source FEM codes (fenics). I have left the top surface to be ...
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1 vote
760 views

### 3D Stationary Wavelet Transform implementations

I'm interested in using a SWT to perform Multi Resolution Analysis over 3D data arrays. However I could not find any software package that implements it. The Matlab Toolbox of wavelets (the most ...
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### What are the most popular wavelet or tight frame regularizers for image reconstruction problems?

A common approach to image reconstruction is to solve the convex optimization problem $$\text{minimize} \quad \frac12 \| Ax - b \|^2 + \gamma \| Dx \|_1$$ where $b$ is a ...
• 181
357 views

### wavelet for numerical partial differential equations

Is there a good introduction into wavelet Galerkin schemes for numerical partial (and ordinary) differential equations?
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125 views

### Spatio-temopral wavelet analysis

Am quite new to wavelet analysis and would like some help. I am performing a spatio-temporal analysis of monthly gridded rainfall data. With PCA, I can reduce the dimension of the rainfall data into a ...
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3k views

### How to compute the wavelet approximation of a function?

For the function $f(x)=x$, how to compute the wavelet approximation using Haar basis? I'm new to wavelet, I'm looking for a package which will do something like this ...
123 views

### Wavelets frame for $L^2[0,\infty)$

I need a wavelet frame for $L^2[0,\infty)$. Moreover, the wavelet should be twice differentiable and with continuous second order derivatives. Hopefully, the wavelet should have compact support (...
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