File:From Continuous To Discrete Fourier Transform.gif

此为最大尺寸。

From_Continuous_To_Discrete_Fourier_Transform.gif ‎（800 × 242像素，文件大小：15 KB，MIME类型：image/gif）

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摘要

描述	English: Relationship between the (continuous) Fourier transform and the discrete Fourier transform. Left column: A continuous function (top) and its Fourier transform (bottom). Center-left column: Periodic summation of the original function (top). Fourier transform (bottom) is zero except at discrete points. The inverse transform is a sum of sinusoids called Fourier series. Center-right column: Original function is discretized (multiplied by a Dirac comb) (top). Its Fourier transform (bottom) is a periodic summation (DTFT) of the original transform. Right column: The DFT (bottom) computes discrete samples of the continuous DTFT. The inverse DFT (top) is a periodic summation of the original samples. The FFT algorithm computes one cycle of the DFT and its inverse is one cycle of the inverse DFT.
日期	2011年12月5日
来源	自己的作品
作者	Sbyrnes321

(* Source code written in Mathematica 6.0, by Steve Byrnes, 2011. I release this code into the public domain. *)
ClearAll["Global`*"]
SetOptions[Plot, Frame -> True, FrameTicks -> None, Axes -> False, PlotRange -> {{-8, 8}, All}];
SetOptions[ListPlot, Frame -> True, FrameTicks -> None, Axes -> False,
   Filling -> Axis, PlotStyle -> None, PlotRange -> {{-8, 8}, All}];
f[x_] := Exp[-(4/3)*\[Pi] x^2];
g[x_] := Exp[-(3/4)*\[Pi] x^2];
repeatedf[x_, p_] := Sum[f[x + n*p], {n, -10, 10}];
repeatedg[x_, p_] := Sum[g[x + n*p], {n, -10, 10}];
plotf = Plot[f[x], {x, -10, 10}, PlotStyle -> Darker[Blue]];
plotg = Plot[g[x], {x, -10, 10}, PlotStyle -> Darker[Red]];
plotrepeatedf = Plot[repeatedf[x, 5], {x, -10, 10}, PlotStyle -> Darker[Blue]];
discreteg = Table[{x, g[x]}, {x, -10, 10, 1/5}];
plotdiscreteg = ListPlot[discreteg, FillingStyle -> Darker[Red]];
discretef = Table[{x, f[x]}, {x, -10, 10, 1/3}];
plotdiscretef = ListPlot[discretef, FillingStyle -> Darker[Blue]];
plotrepeatedg = Plot[repeatedg[x, 3], {x, -10, 10}, PlotStyle -> Darker[Red]];
discreterepeatedf = Table[{x, repeatedf[x, 11/4]}, {x, -12, 12, 1/4}];
plotdiscreterepeatedf = ListPlot[discreterepeatedf, FillingStyle -> Darker[Blue]];
discreterepeatedg = Table[{x, repeatedg[x, 4]}, {x, -12, 12, 4/11}];
plotdiscreterepeatedg = ListPlot[discreterepeatedg, FillingStyle -> Darker[Red]];
finalimg = Show[GraphicsGrid[{{plotf, plotrepeatedf, plotdiscretef, plotdiscreterepeatedf},
    {plotg, plotdiscreteg, plotrepeatedg, plotdiscreterepeatedg}}], ImageSize -> 800]
SetDirectory["C:\\Users\\Steve\\Desktop"];
Export["test.gif", finalimg]

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