
[Science] [BAS home] [Met home] [Beowulf home]	Antarctic Meteorology

Bit comparison

64-bit Atmos-only

On one processor, runs yaaug (MPP 1-proc) and yaauf (non-MPP) bit compare. With an extra mod (qtpos1a.upd) it bit-compares at up to 4x4 processors. A slightly more modern job yabba also compares, as does the even more up-to-date yabga.

See-also: gcom.

Note that all the prognostic fields compare (as they must). Two diagnostics don't perfectly: "Field 176 : Stash Code 4204 : LARGE SCALE SNOWFALL RATE KG/M2/S" and another similar, whose name I forget. The problem occurs at the south pole.

32-bit Atmos-only

yabba bit compares between 1, 2x2 and 3x3 processors in an MPP job. It *doesn't* compare to yabbb (single-proc) job. This is odd, because the same jobs run at 64-bit *do* compare. But I'm not going to fix that now.

yabcc bit compares between 1x2 (run on minifer) and 1x1 (run on bs2140, my cr*ppy P4 2GHz box) out to months. I ran the job as a test of the installation on bs2140.

General

Note: the model is supposed to bit-compare between restarts. Starting from 1-timestep (or 1-hour) staggered dumps, it doesn't. Tim Johns (pers comm) says this doesn't surprise him, and that testing staggered-start bit comparison one should always use day-skips. Using day-skips does work OK.

Past last modified: 21/3/2003 / wmc@bas.ac.uk