FFT and IFFT with FFTW
FFT and IFFT with FFTW
我正在尝试在浮点数组上做 ifft 和 fft。然而,两者的结果是相同的。你有什么想法吗?为什么结果是一样的,即使我对一个使用FFTW_FORWARD,对另一个使用FFTW_BACKWARD?
int N=16;
fftwf_complex in[N], out[N];
fftwf_plan p1, q;
/* prepare a cosine wave */
for (i = 0; i < N; i++) {
in[i][0] = cos(3 * 2*M_PI*i/N);
in[i][1] = 0;
}
/* forward Fourier transform, save the result in 'out' */
p1 = fftwf_plan_dft_1d(N, in, out, FFTW_FORWARD, FFTW_ESTIMATE);
fftwf_execute(p1);
for (i = 0; i < N; i++)
cout << out[i][0] << endl;
fftwf_destroy_plan(p1);
printf("nInverse transform:n");
q = fftwf_plan_dft_1d(N, in, out, FFTW_BACKWARD, FFTW_ESTIMATE);
fftwf_execute(q);
for (i = 0; i < N; i++)
cout << out[i][0] << endl;
fftwf_destroy_plan(q);
您只显示输出箱的真实部分,而忽略虚构的分量。碰巧的是,实部匹配,但虚部不同(它们实际上是复杂的共轭):
#include <iostream>
#include <cmath>
#include "fftw3.h"
using namespace std;
int main()
{
int N=16;
fftwf_complex in[N], out[N];
fftwf_plan p1, q;
for (int i = 0; i < N; i++) {
in[i][0] = cos(3 * 2*M_PI*i/N);
in[i][1] = 0;
}
p1 = fftwf_plan_dft_1d(N, in, out, FFTW_FORWARD, FFTW_ESTIMATE);
fftwf_execute(p1);
for (int i = 0; i < N; i++)
cout << out[i][0] << " + j" << out[i][1] << endl; // <<<
fftwf_destroy_plan(p1);
printf("nInverse transform:n");
q = fftwf_plan_dft_1d(N, in, out, FFTW_BACKWARD, FFTW_ESTIMATE);
fftwf_execute(q);
for (int i = 0; i < N; i++)
cout << out[i][0] << " + j" << out[i][1] << endl; // <<<
fftwf_destroy_plan(q);
return 0;
}
编译并运行:
$ g++ -Wall fftwf.cpp -lfftw3f && ./a.out
3.67394e-16 + j0
1.19209e-07 + j7.34788e-16
-3.67394e-16 + j0
8 + j-7.34788e-16
3.67394e-16 + j0
2.38419e-07 + j7.34788e-16
-3.67394e-16 + j0
1.19209e-07 + j-7.34788e-16
3.67394e-16 + j0
1.19209e-07 + j7.34788e-16
-3.67394e-16 + j0
2.38419e-07 + j-7.34788e-16
3.67394e-16 + j0
8 + j7.34788e-16
-3.67394e-16 + j0
1.19209e-07 + j-7.34788e-16
Inverse transform:
3.67394e-16 + j0
1.19209e-07 + j-7.34788e-16
-3.67394e-16 + j0
8 + j7.34788e-16
3.67394e-16 + j0
2.38419e-07 + j-7.34788e-16
-3.67394e-16 + j0
1.19209e-07 + j7.34788e-16
3.67394e-16 + j0
1.19209e-07 + j-7.34788e-16
-3.67394e-16 + j0
2.38419e-07 + j7.34788e-16
3.67394e-16 + j0
8 + j-7.34788e-16
-3.67394e-16 + j0
1.19209e-07 + j7.34788e-16
有趣的是,FFT和IFFT在数学上几乎相同。它们通常都作为单个例程实现,并带有指示方向(正向或反向)的标志。通常,此标志仅影响 twiddle 因子的虚部的符号。
相关文章:
- Problems with std::cin.fail()
- 应用程序崩溃并显示"symbol _ZdlPvm, version Qt_5 not defined in file libQt5Core.so.5 with link time reference"
- 在 Mac 上使用 CMAKE 将 FFTW 和 FFTWPP 链接到项目中时未定义的符号
- 这对"With a stackless coroutine, only the top-level routine may be suspended."意味着什么
- Boost.TEST with CLion: "Test framework quit unexpectedly"
- 避免碎片化的ClientHellos with OpenSSL (DTLS)
- Issues with Win32 ReadProcessMemory API
- Qt with WinAPI MouseProc
- [[maybe_unused]] with structured_binding?
- Issue with WriteProcessMemory
- OpenCV RTP-Stream with FFMPEG
- "Unable to start debugging. No process is associated with this object." - 在Visual Studio Code中使用GDB
- std::adjacent_difference with std::chrono time_point
- DLL Made with CMake 使程序崩溃
- QtCreator with C 库中的链接器问题
- SHBrowseForFolder with BIF_BROWSEFORCOMPUTER and SHGetPathFr
- specialized std::default_delete with QQmlComponent
- VS2019 - Sudo Remote Debugging on Linux with Cmake project
- Inference pytorch C++ with alexnet and cv::imread image
- FFT and IFFT with FFTW