• Title/Summary/Keyword: Fourier Interpolation Function

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IMPROVED STATIONARY $L_p$-APPROXIMATION ORDER OF INTERPOLATION BY CONDITIONALLY POSITIVE DEFINITE FUNCTIONS

  • Yoon, Jung-Ho
    • Journal of applied mathematics & informatics
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    • v.14 no.1_2
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    • pp.365-376
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    • 2004
  • The purpose of this study is to show that the accuracy of the interpolation method can be at least doubled when additional smoothness requirements and boundary conditions are met. In particular, as a basis function, we are interested in using a conditionally positive definite function $\Phi$ whose generalized Fourier transform is of the form $\Phi(\theta)\;=\;F(\theta)$\mid$\theta$\mid$^{-2m}$ with a bounded function F > 0.

Comparative analysis of methods for digital simulation (디지털 전산모사를 위한 방법론 비교분석)

  • Yi, Dokkyun;Park, Jieun
    • Journal of Digital Convergence
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    • v.13 no.9
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    • pp.209-218
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    • 2015
  • Computer simulation plays an important role for a theoretical foundation in convergence technology and the interpolation is to know the unknown values from known values on grid points. Therefore it is an important problem to select an interpolation method for digital simulation. The aim of this paper is to compare analysis of interpolation methods for digital simulation. we test six different interpolation methods namely: Quartic-Lagrangian, Cubic Spline, Fourier, Hermit, PWENO and SL-WENO. Through digital simulation of a linear advection equation, we analyse pros and cons for each method. In order to compare performance, we introduce accuracy computing and Error functions. The accuracy computing is used well-known $L^1-norm$ and the Error functions are dispersion function, dissipation function and total error function. High-order methods well apply to computer simulation, unfortunately, side-effects (Oscillation) happen.

PERTURBATION OF NONHARMONIC FOURIER SERIES AND NONUNIFORM SAMPLING THEOREM

  • Park, Hee-Chul;Shin, Chang-Eon
    • Bulletin of the Korean Mathematical Society
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    • v.44 no.2
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    • pp.351-358
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    • 2007
  • For an entire function f whose Fourier transform has a compact support confined to $[-{\pi},\;{\pi}]$ and restriction to ${\mathbb{R}}$ belongs to $L^2{\mathbb{R}}$, we derive a nonuniform sampling theorem of Lagrange interpolation type with sampling points ${\lambda}_n{\in}{\mathbb{R}},\;n{\in}{\mathbb{Z}}$, under the condition that $$\frac{lim\;sup}{n{\rightarrow}{\infty}}|{\lambda}_n-n|<\frac {1}{4}$.

Numerical Quadrature Techniques for Inverse Fourier Transform in Two-Dimensional Resistivity Modeling (2차원 전기비저항 모델링에서 후리에역변환의 수치구적법)

  • Kim, Hee Joon
    • Economic and Environmental Geology
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    • v.25 no.1
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    • pp.73-77
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    • 1992
  • This paper compares numerical quadrature techniques for computing an inverse Fourier transform integral in two-dimensional resistivity modeling. The quadrature techniques using exponential and cubic spline interpolations are examined for the case of a homogeneous earth model. In both methods the integral over the interval from 0 to ${\lambda}_{min}$, where ${\lambda}_{min}$, is the minimum sampling spatial wavenumber, is calculated by approximating Fourier transformed potentials to a logarithmic function. This scheme greatly reduces the inverse Fourier transform error associated with the logarithmic discontinuity at ${\lambda}=0$. Numrical results show that, if the sampling intervals are adequate, the cubic spline interpolation method is more accurate than the exponential interpolation method.

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Gravity modeling and application to the gravity referenced navigation (중력모델링과 중력참조항법에의 적용)

  • Lee, Ji-Sun;Kwon, Jay-Hyoun;Yu, Myeong-Jong
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.29 no.5
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    • pp.543-550
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    • 2011
  • The gravity anomaly is a basic geophysical data applied in various fields such as geophysics, geodesy and national defense. In general, the gravity anomaly is used through a interpolation process based on the constructed database. The gravity variation, however, is appeared in various shapes depending on the topography and the density of the underground structures. Therefore, the interpolation could lead to a large differences if the gravity fields do not satisfy the assumptions on the signal behavior like linear or a certain degree polynomials. Furthermore, the interpolation does not reflect the physical characteristics of the gravity such as the harmonic condition. In this study, the gravity modeling using the plane Fourier series and radial basis functions are performed to overcome the problems in the usual interpolation. The results of the modeling is analyzed for the case of the gravity referenced navigation focused on the signal characteristics. Based on the study, it was found that the results from modeling are not much different to that from the interpolation in a smoothly varied area. In case of the highly varied area, however, a large differences are appeared among the three methods. Especially, the Fourier series shows the most smooth variations in the modeled gravity values while the highest variations appeared in the interpolation. Applying to the gravity referenced navigation, it was found that the modeling is more effective in calculation cost. It is considered that the results from this study provides a basis on effective modeling of the gravity fields in terms of the signal characteristics and resolution for various application fields.

An IE-FFT Algorithm to Analyze PEC Objects for MFIE Formulation

  • Seo, Seung Mo
    • Journal of electromagnetic engineering and science
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    • v.19 no.1
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    • pp.6-12
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    • 2019
  • An IE-FFT algorithm is implemented and applied to the electromagnetic (EM) solution of perfect electric conducting (PEC) scattering problems. The solution of the method of moments (MoM), based on the magnetic field integral equation (MFIE), is obtained for PEC objects with closed surfaces. The IE-FFT algorithm uses a uniform Cartesian grid to apply a global fast Fourier transform (FFT), which leads to significantly reduce memory requirement and speed up CPU with an iterative solver. The IE-FFT algorithm utilizes two discretizations, one for the unknown induced surface current on the planar triangular patches of 3D arbitrary geometries and the other on a uniform Cartesian grid for interpolating the free-space Green's function. The uniform interpolation of the Green's functions allows for a global FFT for far-field interaction terms, and the near-field interaction terms should be adequately corrected. A 3D block-Toeplitz structure for the Lagrangian interpolation of the Green's function is proposed. The MFIE formulation with the IE-FFT algorithm, without the help of a preconditioner, is converged in certain iterations with a generalized minimal residual (GMRES) method. The complexity of the IE-FFT is found to be approximately $O(N^{1.5})$and $O(N^{1.5}logN)$ for memory requirements and CPU time, respectively.

Stochastic interpolation of earthquake ground motions under spectral uncertainties

  • Morikawa, Hitoshi;Kameda, Hiroyuki
    • Structural Engineering and Mechanics
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    • v.5 no.6
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    • pp.839-851
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    • 1997
  • Closed-form solutions are analytically derived for stochastic properties of earthquake ground motion fields, which are conditioned by an observed time series at certain observation sites and are characterized by spectra with uncertainties. The theoretical framework presented here can estimate not only the expectations of such simulated earthquake ground motions, but also the prediction errors which offer important information for the field of engineering. Before these derivations are made, the theory of conditional random fields is summarized for convenience in this study. Furthermore, a method for stochastic interpolation of power spectra is explained.

Fast Harmonic Synthesis Method for Sinusoidal Speech-Audio Model (정현파 음성-오디오 모델의 빠른 하모닉 합성 방법)

  • Kim, Gyu-Jin;Kim, Jong-Hark;Jung, Gyu-Hyeok;Lee, In-Sung
    • Journal of the Institute of Electronics Engineers of Korea SP
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    • v.44 no.4 s.316
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    • pp.109-116
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    • 2007
  • Most harmonic synthesis methods using phase information employ a quadratic or cubic phase interpolation. The methods are computationally expensive to implement because every component sinewave must be synthesized on a per sample basis. In this paper, we propose a fast harmonic synthesis method for sinusoidal speech/audio coding based on the quadratic and cubic phase function to overcome the complexity problem. To derive the fast harmonic synthesis method, we define the over-sampling function and phase modulation function by constraining the parameter of phase function to be independent for harmonic index and derive the fast synthesis method using IFFT. Experimental results show that the proposed method significantly reduce the complexity of conventional cosine synthesis method while maintaining the performance.

K-domain Linearization Using Fiber Bragg Grating Array Based on Fourier Domain Optical Coherence Tomography (광섬유 브라그 격자를 이용한 퓨리어 영역 광 결맞음 단층 촬영에서의 파수영역 선형화)

  • Lee, Byoung-Chang;Eom, Tae-Joong;Jeon, Min-Yong
    • Korean Journal of Optics and Photonics
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    • v.22 no.2
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    • pp.72-76
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    • 2011
  • We demonstrate a k-domain linearization using a fiber Bragg grating (FBG) array for Fourier domain optical coherence tomography based on a wavelength swept laser. The k-domain linearization is carried out with an interpolation method using a FBG array with five FBGs. The measured signal-to-noise ratio from the point spread function after k-domain linearization is 12 dB improved over that of without k-domain linearization at the 1 mm depth of the sample. Clear OCT imaging of the slide glass with k-domain linearization could be obtained.

Extraction of a Distance Parameter in Optical Scanning Holography Using Axis Transformation

  • Kim, Tae-Geun;Kim, You-Seok
    • Journal of the Optical Society of Korea
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    • v.14 no.2
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    • pp.104-108
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    • 2010
  • We proposed an axis transformation technique which reveals a distance parameter directly from optical scanning holography (OSH). After synthesis of a real-only spectrum hologram and power fringe adjusted filtering, we transform an original frequency axis to a new frequency axis using interpolation. In the new frequency axis, the filtered hologram has a single frequency which is linearly proportional to the distance parameter. Thus, the inverse Fourier transformation of the filtered hologram gives a delta function pair in the new spatial axis. Finally, we extract the distance parameter by detecting the location of the delta function pair.