ifftn

Multidimensional inverse fast Fourier transform

Syntax

X = ifftn(Y)

X = ifftn(Y,sz)

X = ifftn(___,symflag)

Description

X = ifftn(Y)returns themultidimensional discrete inverse Fourier transform使用快速傅立叶变换算法的N-D阵列。N-D逆变换等于沿着每个维度的1-D逆变换计算Y。输出Xis the same size asY。

example

X = ifftn(Y,sz)truncatesY或者padsY尾随零之前，在根据矢量的元素进行逆变换之前sz。Each element ofszdefines the length of the corresponding transform dimension. For example, ifYis a 5-by-5-by-5 array, thenX = ifftn(Y,[8 8 8])pads each dimension with zeros, resulting in an 8-by-8-by-8 inverse transformX。

example

X = ifftn(___,symflag)specifies the symmetry ofY。For example,ifftn(Y,'symmetric')零食Yas conjugate symmetric.

Examples

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3-D Inverse Transform

打开实时脚本

You can use theifftn功能以将频率采样的多维数据转换为在时间或空间中采样的数据。这ifftnfunction also allows you to control the size of the transform.

Create a 3-by-3-by-3 array and compute its inverse Fourier transform.

y = rand（3,3,3）;ifftn（y）;

Pad the dimensions ofY使用尾随的零，使转换具有8乘8 x 8的尺寸。

X = ifftn(Y,[8 8 8]); size(X)

ans =1×38 8 8

Conjugate Symmetric Array

打开实时脚本

对于几乎共轭对称阵列，您可以通过指定逆傅立叶变换来计算逆傅立叶变换'symmetric'option, which also ensures that the output is real.

Compute the 3-D inverse Fourier transform of a nearly conjugate symmetric array.

Y(:,:,1) = [1e-15*i 0; 1 0]; Y(:,:,2) = [0 1; 0 1]; X = ifftn(Y,'symmetric')

X = X(:,:,1) = 0.3750 -0.1250 -0.1250 -0.1250 X(:,:,2) = -0.1250 0.3750 -0.1250 -0.1250

Input Arguments

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`Y`—Input array
vector|matrix|multidimensional array

Input array, specified as a vector, a matrix, or a multidimensional array. IfYis of typesingle, thenifftnnatively computes in single precision, andXis also of typesingle。否则，Xis returned as typedouble。

`sz`—Lengths of inverse transform dimensions
vector of positive integers

Lengths of inverse transform dimensions, specified as a vector of positive integers.

`symflag`—对称类型
`'nonsymmetric'`(default) |`'symmetric'`

对称类型, specified as'nonsymmetric'或者'symmetric'。WhenYis not exactly conjugate symmetric due to round-off error,ifftn(Y,'symmetric')零食Y好像是共轭对称的。有关共轭对称的更多信息，请参阅Algorithms。

More About

collapse all

N-D Inverse Fourier Transform

这discrete inverse Fourier transformXof anN-D arrayYis defined as

$X_{p_{1}, p_{2}, 。。。, p_{N}} = \sum_{j_{1} = 1}^{m_{1}} \frac{1}{m_{1}} ω_{m_{1}}^{p_{1} j_{1}} \sum_{j_{2} = 1}^{m_{2}} \frac{1}{m_{2}} ω_{m_{2}}^{p_{2} j_{2}} 。。。 \sum_{j_{N} = 1}^{m_{N}} \frac{1}{m_{N}} ω_{m_{N}}^{p_{N} j_{N}} Y_{j_{1}, j_{2}, 。。。, j_{N}} 。$

Each dimension has lengthm_kfork= 1,2,...,N，和 $ω_{m_{k}} = e^{2 π i / m_{k}}$ are complex roots of unity whereiis the imaginary unit.

Algorithms

这ifftnfunction tests whether the vectors in an arrayY在所有维度上都是共轭对称的。向量v当对称时是共轭的ith element satisfiesv(i) = conj(v([1,end:-1:2]))。如果向量中的向量Yare conjugate symmetric in all dimensions, then the inverse transform computation is faster and the output is real.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

对称类型'symmetric'is not supported.
这sz参数必须具有固定的大小。
对于MEX输出，MATLAB^®Coder™使用MATLAB用于FFT算法的库。对于独立的C/C ++代码，默认情况下，代码生成器生成用于FFT算法的代码，而不是生成FFT库调用。要生成针对特定安装的FFTW库的呼叫，请提供FFT库回调类。有关FFT库回调类的更多信息，请参阅coder.fftw.StandaloneFFTW3Interface。
For simulation of aMATLAB Functionblock, the simulation software uses the library that MATLAB uses for FFT algorithms. For C/C++ code generation, by default, the code generator produces code for FFT algorithms instead of producing FFT library calls. To generate calls to a specific installed FFTW library, provide an FFT library callback class. For more information about an FFT library callback class, seecoder.fftw.StandaloneFFTW3Interface。

Documentation

ifftn

Syntax

Description

Examples

3-D Inverse Transform

Conjugate Symmetric Array

Input Arguments

`Y`—Input array
vector|matrix|multidimensional array

`sz`—Lengths of inverse transform dimensions
vector of positive integers

`symflag`—对称类型
`'nonsymmetric'`(default) |`'symmetric'`

More About

N-D Inverse Fourier Transform

Algorithms

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

See Also

在R2006a之前引入

MATLAB Documentation

万博1manbetx

Try MATLAB, Simulink, and Other Products

Documentation

ifftn

Syntax

Description

Examples

3-D Inverse Transform

Conjugate Symmetric Array

Input Arguments

Y—Input arrayvector|matrix|multidimensional array

sz—Lengths of inverse transform dimensionsvector of positive integers

symflag—对称类型'nonsymmetric'(default) |'symmetric'

More About

N-D Inverse Fourier Transform

Algorithms

Extended Capabilities

C/C++ Code GenerationGenerate C and C++ code using MATLAB® Coder™.

See Also

在R2006a之前引入

MATLAB Documentation

万博1manbetx

Try MATLAB, Simulink, and Other Products

`Y`—Input array
vector|matrix|multidimensional array

`sz`—Lengths of inverse transform dimensions
vector of positive integers

`symflag`—对称类型
`'nonsymmetric'`(default) |`'symmetric'`

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.