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====== Fast Fourier Transform (FFT) ====== | ====== Fast Fourier Transform (FFT) ====== | ||
- | Open table with initial data and use '' | + | Open Table or Figure or Plot with initial data and use '' |
- | {{:fft1.png|}} | + | 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. |
- | ===== Formulas ===== | + | {{:fft.png? |
- | MagicPlot uses ' | + | |
- | Here < | + | ===== Parameters ===== |
- | ^ | + | ^ Sampling Interval |
- | ^ | + | ^ Real, \\ Imaginary |
- | ^ | + | ^ Forward / \\ Inverse |
+ | ^ 1/N in forward transform | ||
+ | ^ 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:// |
- | ===== Parameters | + | ==== Discrete Fourier Transform Formulas |
- | ^ Sampling Interval | + | By default MagicPlot uses ' |
- | ^ Real \\ Imaginary | + | |
- | ^ Forward \\ Inverse | + | ^ Factor −1 (Default) |
- | ^ Normalize forward transform | + | ^ 1/N in forward \\ transform |
- | ^ Center zero frequency | + | ^ Checked \\ (Default) |
+ | ^ | ||
+ | |||
+ | \\ | ||
+ | |||
+ | ^ Factor +1 (Scientific) | ||
+ | ^ 1/N in forward \\ transform | ||
+ | ^ Checked \\ (Default) | ||
+ | ^ Unchecked | ||
+ | |||
+ | |||
+ | Here // | ||
+ | |||
+ | Note: if you expect to get the original data when doing an inverse FFT of forward FFT, set the '' | ||
+ | |||
+ | ==== Amplitude and Phase Columns Formulas ==== | ||
+ | < | ||
+ | |||
+ | Because of using '' | ||
+ | |||
+ | ==== Sampling Column Formulas ==== | ||
+ | Sampling column contains frequency samples if forward transform is performed and time samples in case of inverse transform. | ||
+ | ^ Center zero \\ frequency | ||
+ | ^ Unchecked | ||
+ | ^ | ||
+ | Here Δ//t// is given sampling interval | ||
+ | |||
+ | ==== Missing Values in the Original Data ==== | ||
+ | Fourier transform | ||
+ | |||
+ | * Missing values | ||
+ | |||
+ | * Missing values in the end of the column are ignored. | ||
+ | |||
+ | ===== See Also ===== | ||
+ | * [[processing]] |