Ifftcalculates the discrete inverse Fourier transform of the sequence in the arrayFand stores the result in the arrayA.Lognis the base-2 log of the number of points in the sequences. The arrayFmust contain at least 2Logn-1 elements; the arrayAmust contain at least 2Lognelements. If the arrays have more than the required number of elements, the extra elements are ignored and unmodified. The number of elements inAdenoted by each permitted value ofLognis shown in the table below:
Logn No. Elements (2Logn)
2 4
3 8
4 16
5 32
6 64
7 128
8 256
9 512
10 1024
11 2048
12 4096
13 8192
14 16384
The values input toIfftare in the same format as those output by theFftroutine. See the entry forFftfor a detailed explanation of the meaning of the values returned byIfft.
Errors
Ifftcauses an HTBasic error if its arguments are not of the types shown in the USAGE section, above, ifLognis not between 2 and 15, inclusive, or if the size ofAorFis smaller than the values explained above.