Table 1. PIPER run times for one rotation using a single core of a 2008 2 GHz quad-core Xeon processor.

Phase	Run time (s)	% total
ligand rotation	0.00	0
charge assignment	0.23	2.3
FFT of ligand grids	4.51	45.4
modulation of grid pairs	0.22	2.2
IFFT of ligand grids	4.51	45.4
accumulation of desolvation terms	0.24	2.4
scoring and filtering	0.23	2.3
Total	9.94	100

P = 18 so 22 correlations are computed. Steps performed once are negligible over thousands of iterations