AmberFF_test fails intermittently

[dstoeckel]

The AmberFF_test sometimes fails with the following error message (the numbers are always the same):

checking [EXTRA] Additivity of energies w/ selection... 
    (line 511 TEST_REAL_EQUAL(r4_r1 - r4_i, r1_r4 - r1_i): got -145.471, expected -103.957)  - 
    (line 513 TEST_REAL_EQUAL(r1_r4 - r1_i + r1_tpl + r4_tpl + tpl_i, total_energy): got 1680.36, expected 1638.84)  - 
    FAILED

This hints at some non-determinism in the Amber code, that might be triggered by something like pointers in a HashMap, etc.

Tested on Ubuntu 14.04.

[tkemmer]

I had the same problem yesterday under Gentoo (same numbers):

checking [EXTRA] Additivity of energies w/ selection... 
    (line 511 TEST_REAL_EQUAL(r4_r1 - r4_i, r1_r4 - r1_i): got -145.471, expected -103.957)  - 
    (line 513 TEST_REAL_EQUAL(r1_r4 - r1_i + r1_tpl + r4_tpl + tpl_i, total_energy): got 1680.36, expected 1638.84)  - 
    FAILED
FAILED

So far, this only happened once and only with my current working copy of the master branch (incremental build processes), not with clean builds. The latter might be a coincidence, though.

[anhi]

I think this is a rather bad one – not sure yet, but I believe that it is an effect of the setup-handling. Selection is handled differently based on whether it was switched on before or after the call to setup. Calling select before setup will remove all non-selected atoms from the force field entirely. Calling it after setup will compute the energies and forces only on selected atoms, but based also on non-selected atoms. This mechanism is, unfortunately, based on time stamps. If the clock rewinds after calling setup, the logic screws up. We need to fix this, but I don’t think it is a regression, so should not block 1.5.

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Betreff: Re: [BALL-Project/ball] AmberFF_test fails intermittently (#584)

I had the same problem yesterday under Gentoo (same numbers):

checking [EXTRA] Additivity of energies w/ selection...
(line 511 TEST_REAL_EQUAL(r4_r1 - r4_i, r1_r4 - r1_i): got -145.471, expected -103.957) -
(line 513 TEST_REAL_EQUAL(r1_r4 - r1_i + r1_tpl + r4_tpl + tpl_i, total_energy): got 1680.36, expected 1638.84) -
FAILED
FAILED

So far, this only happened once and only with my current working copy of the master branch (incremental build processes), not with clean builds. The latter might be a coincidence, though.

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[dstoeckel]

Nevertheless we should probably fix the test. I am not sure if this is an issue on the CI servers, but I imagine that randomly failing builds are no fun.

If it is really a timestamp issue we could add short sleeps between select and setup to decrease the likelyhood of things breaking. In Amber we could check the timestamps for non-monotonicity and at least issue a warning.

[philthiel]

According to Daniels suggestion I added a fix that reduces the number of test failures roughly about ten times (d5c8f85).