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Table 1

Computational performance of our fastest A-Projection implementation described in Sects. 3.3 and 4.4.3.

N pix d D N stokes w max N S N W Δtν t CF t grid t el t W Memory
(deg) (km) (s, MHz) (h, MHz) (%) (%) (%) (%) (Gb) (s)

1024 40 11.4 IQUV 20 15 14 300, 0.78 3, 3.5 67.8 10.2 19.7 2.1 1 40.9
4096 10 11.4 IQUV 20 15 14 300, 0.78 3, 3.5 24.5 4.9 57.5 12.8 4.5 117.4
4096 10 11.4 I 20 15 14 300, 0.78 none 52.0 11.4 0.0 36.5 1.5 143.7
8192 5 11.4 I 20 15 14 300, 0.78 none 32.8 6.1 0.0 60.9 6.1 335.7

Notes. Columns list various performance parameters corresponding to different imaging settings. The tests were performed for a 12 sub-band dataset (1 channel per sub-band) on the CEP2 LOFAR cluster node each having 24 AMD Opteron(tm) 6172 Processors, and 64 Gb of RAM memory. is the total time for a gridding or degridding step. The times tCF, tgrid, tel, and tW are given as fractions of , and they correspond to the times needed to compute convolution functions, grid/degrid the data, apply the element beam and apply the W-term, respectively. We are confident we can still gain a factor of  ≳ 2–4 in time over these values.

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