Regularization fixes + switch for the pre-PR-15610 compatibility mode - #15784
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DCAFitter: apply X-error regularization only where it is needed, drop duplications
Follow-up to PR15610. The fitted PCA and chi2 are unchanged; the vertex covariance
returned by calcPCACovMatrix() (and hence by createParentTrackParCov()) becomes larger
along weakly constrained directions.
1. TrackCovI::set() takes the regularization strength as an argument (XRegErrFactor
by default, XRegNone to disable). The weak dummy X error added to sxx is needed
only to keep the Newton Hessian invertible for (nearly) collinear prongs, so
calcPCACovMatrix() now rebuilds the information matrices with XRegNone: there
only their sum is inverted (and an ill-conditioned sum is already replaced by a
loose dummy), hence the prior would only make the longitudinal vertex error
follow the dummy XRegErrFactor*Cyy instead of the track slopes. Documented in
DCAFitterN_derivation.md.
2. createParentTrackParCov() uses getCovXYZPxPyPzGlo() again instead of the
hand-written momentum Jacobian, which was algebraically identical to it (same
J for the native snp,tgl,q/pt parameters, same |q/pt|/|snp| guard). Also
replaced the literal 21 by o2::track::kLabCovMatSize.
3. The M*E*M^T rotate-and-sum block, identical in calcInverseWeight() and
calcPCACovMatrix(), is factored into addRotatedTrackInfo(). This replaces the
now unused getTrackRotMatrix().
4. calcCollinearInflation() uses o2::gpu::GPUCommonMath instead of host-only
std::sqrt/clamp/max/min, so it stays device-compilable although currently not
called; its commented-out call site becomes an explicit TODO and the unused
InflateRelDet/MaxInflation constants are removed.
5. correctTracks() sets mPropFailed and logs via mLoggerBadProp on a failed
propagation, as propagate{Param}ToX() do; the commented-out Taylor block is
replaced by a comment on why mCandTr must be moved and why the analytic
constant-Bz transport is used for the small Newton steps.
6. Added the missing newline to the mLoggerBadPCACov message.
Verified by a full explicit instantiation of DCAFitterN<2>/<3>, which type-checks
all members including the otherwise uninstantiated calcCollinearInflation().
Co-Authored-By: Claude Opus 5
Collaborator
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Error while checking build/O2/fullCI_slc9 for edb2171 at 2026-09-10 14:55: Full log here. |
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If isOldMode() is true (default), the behavior of the DCAFitter will reproduce the pre-PR-15610 version. One can swith any time (before calling DCAFitter::process(..)) between the modes via DCAFitter::setOldMode(bool v). In the o2-secondary-vertexing-workflow and related study workflows it can be steered by the svertexer.oldDCAFitterMode=true (default) configurable param.
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Do not squash, the compatibility mode (2nd commit) might be temporary.