Optimization of a parallel pseudospectral MHD code

In this article we outline some techniques for optimizing spectral codes using multidimensional real-to-complex FFT's. We have successfully applied these techniques on a pseudospectral MHD code running on the CRAY T3E. The code uses half precision, and runs up to 2.5 times faster than the version that uses full precision CRAY SCILIB parallel FFT routines. The half precision version without these optimizations is slower does not scale very well, and cannot support more than 128 processors. The optimized code achieved a performance of 100 Gflops on 1024 nodes of a CRAY T3E-600 at NASA Goddard Space Flight Center.