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The FFTW version 2 libraries on HECToR are only available for the Portland Group compiler, so the full FFT comparison tests were performed exclusively with pgf90. Cray's LibSci (10.2.1) was used for BLAS and LAPACK. The following compiler flags were used throughout the FFT tests:

-fastsse -O3 -Mipa

In order to measure the performance of the FFT routines specifically we used Castep's internal Trace module to profile the two subroutines wave_recip_to_real_slice and wave_real_to_recip_slice. These subroutines take a group of eigenstates, called a wavefunction slice, and Fourier transform them from reciprocal space to real space, or vice versa.

Figure 3.1: Graph showing the relative performance of the four FFT subroutines available to Castep on HECToR for the TiN benchmark. This benchmark transforms wavefunction slices to real space 1634 times and back again.

As can be seen from figure 3.1 FFTW 3.1.1 was the fastest FFT library available on HECToR.

Sarfraz A Nadeem 2008-09-01