SFTPACK
"Slow" Fourier Transforms

SFTPACK, a MATLAB library which carries out some "slow" Fourier transforms, that is, Fourier transforms without the techniques that allow for very fast computation.

The intention is to make the underlying calculation clear, and to provide a simple check and comparison of timing and usage for the fast calculations.

The fast Fourier transform is a highly efficient procedure. However, the coding of the algorithm, and the conventions for indexing, ordering, and normalization, can make it quite difficult to understand what is being done, or even to see how to use the software correctly. This means that a coding error or mistaken use can be undetected.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

SFTPACK is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

Related Data and Programs:

C8LIB, a MATLAB library which implements certain elementary functions for double precision complex variables;

COSINE_TRANSFORM, a MATLAB library which demonstrates some simple properties of the discrete cosine transform (DCT).

FFT_SERIAL, a MATLAB program which demonstrates the computation of a Fast Fourier Transform, and is intended as a starting point for implementing a parallel version.

HAAR, a MATLAB library which computes the Haar transform of data.

sftpack_test

SINE_TRANSFORM, a MATLAB library which demonstrates some simple properties of the discrete sine transform.

WALSH, a MATLAB library which implements versions of the Walsh and Haar transforms.

WAVELET, a MATLAB library which does some simple wavelet calculations;

Reference:

1. William Briggs, Van Emden Henson,
   The DFT: An Owner's Manual for the Discrete Fourier Transform,
   SIAM, 1995,
   ISBN13: 978-0-898713-42-8,
   LC: QA403.5.B75.
2. Ralph Hartley,
   A More Symmetrical Fourier Analysis Applied to Transmission Problems,
   Proceedings of the Institute of Radio Engineers,
   Volume 30, 1942, pages 144-150.

Source Code:

• c8mat_print_some.m, prints some of a C8MAT.
• c8mat_sftb.m, computes a "slow" backward Fourier transform of a C8MAT.
• c8mat_sftf.m, computes a "slow" forward Fourier transform of a C8MAT.
• c8mat_uniform_01.m, returns a unit pseudorandom C8MAT.
• c8vec_print_part.m, prints part of a C8VEC.
• c8vec_sftb.m, computes a "slow" backward Fourier transform of a C8VEC.
• c8vec_sftf.m, computes a "slow" forward Fourier transform of a C8VEC.
• c8vec_uniform_01.m, returns a unit pseudorandom C8VEC.
• i4_modp.m, returns the nonnegative remainder of integer division;
• i4_wrap.m, forces an integer to lie between given limits by wrapping.
• r8vec_permute_cyclic.m, cyclically permutes an R8VEC;
• r8vec_print.m, prints an R8VEC.
• r8vec_print_part.m, prints "part" of an R8VEC.
• r8vec_sct.m, computes a "slow" forward or backward cosine transform of an R8VEC.
• r8vec_sftb.m, computes a "slow" backward Fourier transform of an R8VEC.
• r8vec_sftf.m, computes a "slow" forward Fourier transform of an R8VEC.
• r8vec_sht.m, computes a "slow" forward or backward Hartley transform of an R8VEC.
• r8vec_sqctb.m, computes a "slow" backward quarter cosine transform of an R8VEC.
• r8vec_sqctf.m, computes a "slow" forward quarter cosine transform of an R8VEC.
• r8vec_sqstb.m, computes a "slow" backward quarter sine transform of an R8VEC.
• r8vec_sqstf.m, computes a "slow" forward quarter sine transform of an R8VEC.
• r8vec_sst.m, computes a "slow" forward or backward sine transform of an R8VEC.
• r8vec_swtb.m, computes a "slow" backward wavelet transform of an R8VEC.
• r8vec_swtf.m, computes a "slow" forward wavelet transform of an R8VEC.
• r8vec_uniform_ab.m, returns a scaled pseudorandom R8VEC.
• timestamp.m, prints the current YMDHMS date as a time stamp.