In addition to the Fast Fourier Transform (FFT) interface, described in Fast Fourier Transforms, Intel® MKL supports the Real Discrete Trigonometric Transforms (sometimes called real-to-real Discrete Fourier Transforms) interface. In this manual, the interface is referred to as TT interface. It implements a group of routines (TT routines) used to compute sine/cosine, staggered sine/cosine, and twice staggered sine/cosine transforms (referred to as staggered2 sine/cosine transforms, for brevity). The TT interface provides much flexibility of use: you can adjust routines to your particular needs at the cost of manual tuning routine parameters or just call routines with default parameter values. The current Intel MKL implementation of the TT interface can be used in solving partial differential equations and contains routines that are helpful for Fast Poisson and similar solvers.
To describe the Intel MKL TT interface, the C convention is used. Fortran users should refer to Calling PDE Support Routines from Fortran 90.
For the list of Trigonometric Transforms currently implemented in Intel MKL TT interface, see Transforms Implemented.
If you have got used to the FFTW interface (www.fftw.org), you can call the TT interface functions through real-to-real FFTW to Intel MKL wrappers without changing FFTW function calls in your code (refer to FFTW to Intel® MKL Wrappers for FFTW 3.x for details). However, you are strongly encouraged to use the native TT interface for better performance. Another reason why you should use the wrappers cautiously is that TT and the real-to-real FFTW interfaces are not fully compatible and some features of the real-to-real FFTW, such as strides and multidimensional transforms, are not available through wrappers.
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