|Description||The Fourier transform of MX is calculated and stored in MY. The forward transform is obtained by setting dir = 1, the inverse (or backward) transform by setting dir = -1. A Fast Fourier Transform algorithm is used that requires both ht and len to be powers of 2.
Complex version: Both MX and the output MY are complex matrices.
Real-to-complex version: The input matrix MX is real. The output matrix MY is complex. As this function can only perform a forward transform, no argument "dir" is needed.
Purely real version: For the forward transform, MX is a real matrix. The output MY is also defined as fMatrix, although it consists of complex numbers. The reason is that, just as in the one-dimensional case, the symmetry properties of two-dimensional FFT allow to store the result in a packed format, fitting into the same memory space as the input matrix. The order of storage in MY is derived from the ordering in the one-dimensional case, with the packing applied first to all rows, then to the columns. The resulting order is indicated in the following table. U means the uncompressed result.
For inverse real-matrix FFT, the input matrix has to be of this packed-complex format, and you get a real matrix. If you prefer to get the result of forward FFT as a true complex matrix, use MF_FFTtoC.
About special versions with the prefixes MFs_, MFl_, and MFp_, consult chapter 4.8.