We used the standard timing values produced by the considered code. Fourier space calculations together with FFT and inverse FFT, and spectral space calculations . The grid point space calculations represent the most important part of the computational work. This way of vectorisation is considered a best case model. It is used to obtain our main result.
All parameters are in ms .
The start-up time of the vector unit is modelled by terms showing 128 as denominator. As an alternative worst case model, we also used vectorisation in direction of longitudes or latitudes only from one boundary to the opposite boundary. Since the C90 hardware does not allow to start vector operations for more than 128 elements at once, there is no big difference between our models in the case of large examples. Since this effect is observed for 16 processors of a single system as well as for the 32 or 64 processors of a cluster, there was no big difference in terms of cluster efficiency. Therefore, we decided to discuss the best case model only throughout this paper.