Chi2MeasurementEstimator

• we are copying and destroying a good amount of clhep matrices and vectors
  • within RecHit2DLocalPos::projectionMatrix(called by GenericTransientTrackingRecHit::projectionMatrix), which returns a copy of the trackingRecHit_->projectionMatrix(). Can we return a const ref ?
  • idem RecHit2DLocalPos::parameters, it returns a copy ... const ref ?

TkStripMeasurementDet::recHits()

22% of the time foes into TkStripMeasurementDet::recHits. of which 15% in StriupCPEfromTrackAngle::localParameters(cluster, LocalTrajectoryParameters)... can we optimize it ? (not easy ... apparently it has real things to do)

Main stuff

• 7% in pow(x,2)!!
• 8% in project
• 18% in creating and destroying CLHEP vectors
• 28% in CLHEP::solve() (of which half in CLHEP copy constructors!) (for a 2x2 linear equation system !!!!!!!!!!!)

Other nice stuff:

• we compute both sin() and cos() of the same angle ... maybe there is no need (besides, is there a c++ function that computes sin and cos with the correct signs in one step ? there is an x87 opcode for this, so I'm surprised of not finding the function....)

Now I'm trying to replace: pow(x,2) with

template <class T> inline const T sqr(const T a) { return a*a; } 

(but I'm not sure if the inlining is done ... otherwise I should fit the result in a temporary variable and do x*x by hand)

Also, I'm replacing CLHEP with SMatrix ... even if the 2x2 system can be probably simplified, optimized and solved by hand

-- GiovanniPetrucciani - 05 Apr 2007