FFT

A number of Figaro functions are available to manipulate complex data, generally with a view to its being used for some process involving Fourier transforms. While there are packaged Figaro routines, such as `scross', which make use of Fourier transforms internally, the functions covered in this section perform the more elementary operations, and can be put together to form a sequence of operations that duplicates the processing performed by, say, `scross', but enabling a finer control to be exercised over the details of the procedure. The general design of this set of routines is based on those provided as part of the SDRSYS system (Straede, 1985). In these notes the term `Fourier transform' is used rather freely; it should be realised that in all cases it is the discrete Fourier transform that is meant.

In Figaro 3.0 the structure of complex data files was changed slightly. Prior to Figaro 3.0, such files contained the modulus of the data as the main data array and held the real and imaginary parts separately. From Figaro 3.0 onwards, the modulus is no longer held as a distinct item, the main data array is the real part of the data, and the imaginary part is still held separately. In practice this should make little difference to the use of these routines, although it does mean that a complex file created by Figaro 2.4 or earlier will not be handled properly by Figaro 3.0. In Figaro 5.1 the format for complex data is changed again slightly. The reason all these changes should make little difference is that complex files are normally intermediate files and are not retained over a long period.