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BaseCluster: initialise errors to 0 by default - #15988

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f3sch merged 2 commits into
AliceO2Group:devfrom
hyungjun-lee:checkresid-pv-sigmayz
Oct 20, 2026
Merged

f3sch merged 2 commits into
AliceO2Group:devfrom
hyungjun-lee:checkresid-pv-sigmayz

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@hyungjun-lee

@hyungjun-lee hyungjun-lee commented Oct 20, 2026 •

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Updated following review: errors are now zero-initialised in BaseCluster itself instead of setting sigmaYZ in CheckResid.

o2::BaseCluster<float> has a defaulted constructor, so mSigmaYZ is left uninitialised. In CheckResidSpec::processITSTrack, with addPVAsCluster enabled, the PV pseudo-cluster bcPV sets X/Y/Z, sigmaY2, sigmaZ2 and the sensor ID but never sigmaYZ. The PV then enters the refit with an arbitrary YZ covariance term taken from the stack.

Default member initialisers only: no change to the data layout (ClassDef version kept), configuration or output format.

o2::BaseCluster default constructor leaves mSigmaYZ uninitialised, so with
addPVAsCluster the PV cluster entered the refit with a garbage YZ covariance
term, making the residuals non-reproducible between identical runs.

@shahor02 shahor02 left a comment

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Thanks, but I think it is better to init to 0 by default Base cluster errors.

Following review: rather than setting sigmaYZ explicitly in CheckResid,
zero-initialise mSigmaY2/mSigmaZ2/mSigmaYZ in BaseCluster so that
default-constructed clusters (e.g. the PV pseudo-cluster in CheckResid)
never carry uninitialised error terms.
@hyungjun-lee hyungjun-lee changed the title CheckResid: initialise sigmaYZ of the PV pseudo-cluster BaseCluster: initialise errors to 0 by default Oct 20, 2026
@hyungjun-lee

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@shahor02,
Thanks for your feedback
I have modified the code following your advice. :D

@f3sch
f3sch merged commit 121fbac into AliceO2Group:dev Oct 20, 2026
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3 participants