This is the README file of the ggfft library

This library is a simple parallel FFT library for data distributed on a M-dimensional toroidal network of 
p_1 x... x p_M processes.  It combines a serial N-dimensional (N>M) FFT (serial_multidim_fft), which is a slight
modification of the Numerical Recipes function "fourn", together with a generalized transposition (transpose()), that
exchange the data with MPI.  No HW specific optimization is attempted, neither in the serial FFT step, nor in the
transposition. I wrote it because I could not find any reliable FFT for a torus of general dimension M in which
N-dimensional (N>M) data are distributed.

Compiling the library:
edit Makefile if necessary (compilers etc...)
make

Using the library:
The user should declare a plan:
    gg_plan myplan;
and call three routines:
    gg_init_plan(&myplan,...) for each plan to be used
    gg_distributed_multidim_fft(&myplan,...), which actually does the FFT
    gg_destroy_plan(&myplan,...) to free the allocated memory
The user should also include the header file "ggfft.h" and link the executable to libggfft.a


Limitation:
-No optimization on the serial FFT is attempted (it is essentially the fourn routine of Numerical Recipes)
-The serial FFT is limited to data lengths of power of 2.
-communication in transpose does not really exploit the topology of the torus.
-dimension of the data should be larger than the dimension of the torus.