Trace:

fft

This shows you the differences between two versions of the page.

Both sides previous revision Previous revision Next revision | Previous revision | ||

fft [Fri Nov 5 12:32:12 2010] Gray |
fft [Thu Jan 14 17:14:11 2021] (current) Alexander |
||
---|---|---|---|

Line 1: | Line 1: | ||

- | ====== Fast Fourier Transform (FFT) (Pro edition only) ====== | + | ====== Fast Fourier Transform (FFT) ====== |

Open Table or Figure or Plot with initial data and use '' | Open Table or Figure or Plot with initial data and use '' | ||

Fast Fourier transform algorithm computes discrete Fourier transform exactly and is used to considerably speed up the calculations.\\ Note that FFT is not an approximate method of calculation. | Fast Fourier transform algorithm computes discrete Fourier transform exactly and is used to considerably speed up the calculations.\\ Note that FFT is not an approximate method of calculation. | ||

- | MagicPlot uses the algorithm of FFT that does not necessarily require the number of points //N// to be an integer power of 2, though in such a case evaluation is faster. MagicPlot uses [[http://www.netlib.org/|jfftpack]] library (a Java version of fftpack). | + | {{:fft.png?nolink|}} |

- | | {{:fft1.png|FFT of table columns dialog}} | {{:fft2.png|FFT of curves dialog}} | | + | ===== Parameters ===== |

+ | | ||

+ | ^ Sampling Interval | Sampling interval of original data Δ//t// is used to compute the data in resulting sampling column. MagicPlot calculates sampling interval as a difference between second and first values in ''| | ||

+ | ^ Real, \\ Imaginary of data. \\ If your data is purely real, select ''< | ||

+ | ^ Forward / \\ Inverse | ||

+ | ^ 1/N in forward transform table). If your original data is real, you may want to additionally multiply the result by 2 to get the true amplitudes of real signal. Also referred as ''| | ||

+ | ^ Center zero frequency . | | ||

+ | | ||

+ | ===== Algorithm ===== | ||

+ | | ||

+ | MagicPlot uses the algorithm of FFT that does not necessarily require the number of points //N// to be an integer power of 2, though in such a case evaluation is faster. MagicPlot uses [[http://|jfftpack]] library (a Java version of fftpack). | ||

- | ===== Formulas ===== | ||

==== Discrete Fourier Transform Formulas ==== | ==== Discrete Fourier Transform Formulas ==== | ||

By default MagicPlot uses ' | By default MagicPlot uses ' | ||

Line 30: | Line 39: | ||

==== Amplitude and Phase Columns Formulas ==== | ==== Amplitude and Phase Columns Formulas ==== | ||

- | <m>Amplitude_n = sqrt{{Re_n}^2 + {Im_n}^2},Phase_n = atan2(Im_n, | + | <m>A_n = sqrt{{Re_n}^2 + {Im_n}^2},phi_n = atan2(Im_n, |

- | Because of using [[wp> | + | Because of using ''[[wp>'' function the phase is unwrapped and is in range (//. The result of ''. |

==== Sampling Column Formulas ==== | ==== Sampling Column Formulas ==== | ||

Line 48: | Line 57: | ||

* Missing values in the end of the column are ignored. | * Missing values in the end of the column are ignored. | ||

- | ===== Parameters ===== | + | ===== See Also ===== |

- | ^ Sampling Interval | + | * [[processing]] |

- | ^ Real, \\ Imaginary | + | |

- | ^ Forward / \\ Inverse | + | |

- | ^ 1/N in forward transform | + | |

- | ^ Center zero frequency | | + |

fft.1288949532.txt.gz · Last modified: Sun Nov 8 12:20:32 2015 (external edit)

Except where otherwise noted, content on this wiki is licensed under the following license: CC Attribution-Share Alike 4.0 International