[gmx-users] Bug in 3.1.5_beta Altivec?

Choon Peng cpchng at bii.a-star.edu.sg
Fri Jan 17 08:03:21 CET 2003

Dear all,

  Anyone came across funny numerical results obtained from version
3.1.5_beta on G4 using Altivec?
For a NPT simulation (NVT is OK), I actually got a value of
200 bar for pressure while the same beta installed on a PIII cluster
gave the more acceptable result of 3.8 (correct result is 2.3)!
Also, quantities like total energy, temperature, etc are also quite
way off.

Initially I suspected there's general bugs in the beta release but
after confirming with a PIII (using SSE) installation, the prime
suspect is now the Altivec calculations. I know they're faster than in
3.1.4 due to more tuning and will inaccuracies creep in as a result of
too aggressive tuning for performance?


Mr. Choon-Peng CHNG
Scientific Programmer
BioInformatics Institute (BII), A*STAR
21, Heng Mui Keng Terrace, Rm 03-53, Singapore 119613
Tel (O): (65) 68746173 Fax (O): (65) 67781250

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