Behaviour
It computes the Fast Fourier Transform of a measure array. Measures can be OPH_COMPLEX_DOUBLEs (default) or OPH_DOUBLEs (in which case zero imaginary parts will be considered). The output type will always be OPH_COMPLEX_DOUBLE. There are no particular restrictions on the number of input elements but the highest performances can be obtained with numbers that can be factored out as a product of 2,3,4,5,6 or 7. If Delta represents the sampling step, output indexes correspond to particular frequencies according to the following schema:
| index | z | x = FFT(z) |
|---|---|---|
| 0 | z(t = 0) | x(f = 0) |
| 1 | z(t = 1) | x(f = 1/(n Delta)) |
| 2 | z(t = 2) | x(f = 2/(n Delta)) |
| . | ........ | .................. |
| n/2 | z(t = n/2) | x(f = +1/(2 Delta),-1/(2 Delta)) |
| . | ........ | .................. |
| n-3 | z(t = n-3) | x(f = -3/(n Delta)) |
| n-2 | z(t = n-2) | x(f = -2/(n Delta)) |
| n-1 | z(t = n-1) | x(f = -1/(n Delta)) |
When n is even the location n/2 contains the equivalent frequencies (+1/(2* Delta), -1/(2* Delta)). If n is odd then the general structure of the table remains valid, but n/2 does not appear.
Parameters
Return type
Binary-array.
Examples
Compute the coefficients of the FFT of the input measures.
oph_gsl_fft('OPH_COMPLEX_DOUBLE','OPH_COMPLEX_DOUBLE',measure)
Operation type
Simple.
| Argument name | Type | Mandatory | Values | Default | Min/Max-value | Min/Max-times |
|---|---|---|---|---|---|---|
| input measure type | “oph_type” | “yes” | “‘oph_double’|’oph_complex_double’” | “1” / “1” | ||
| output measure type | “oph_type” | “yes” | “‘oph_complex_double’” | “1” / “1” | ||
| measure | “binary-array” | “yes” | “1” / “1” |