The tracking of the first track of Run 1 (the second run) is different for the debug and optimised versions (only) on Linux since the tag exampleN02-V02-00-00 (November 2000). . In the directory /afs/cern.ch/sw/geant4/stt/testlogs/logs accessible to members of geant4 (zb:collaborators) the results of the system testing of examples/novice/N02 diverged on Linux for the optimised and debug code. This was first seen for tagset 192 corresponding to the introduction of ./examples/novice/N02 exampleN02-V02-00-00 and ./source/geometry/magneticfield field-V02-00-01 ./source/geometry/management geommng-V02-00-02 ./source/materials materials-V02-00-01 and has remained. The file sizes are enough to show the results are different. tkdiff is quite useful for comparing outputs. . 274574 Nov 10 04:18 stt.geant4-02-00-cand-01+tags191/Linux-g++.debug/test102.out 274574 Nov 10 04:03 stt.geant4-02-00-cand-01+tags191/Linux-g++.optim/test102.out 266196 Nov 10 15:41 stt.geant4-02-00-cand-01+tags192/Linux-g++.debug/test102.out 393632 Nov 10 15:06 stt.geant4-02-00-cand-01+tags192/Linux-g++.optim/test102.out
It has been verified that output is perfectly reproducible on gcc-3.2 if one associates chip's specific compilation options of the kind (for Pentium-4): -march=pentium4 -mfpmath=sse which forces the usage of the SSE unit for scalar floating-point arithmetics which is said to solve some numerical instability problems happening in the default 387 floating-point coprocessor, where temporaries are handled in 80bit precision.
