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I think this code can behave badly in special cases. I think it's used to calculate, generally, an intercept point in 3D space between a helix and an arbitrary plane. I had issues when the track momentum was too low which I presume meant that the track actually never intercepted the plane anywhere. My memory fails to tell me if this is the error I got. I think I fixed that problem in the MS code by checking analytically if the helix would intercept the plane and only if that was true use this (iterative) method to find the true intercept point. This might be an edge case of some kind in that process but I'm a little surprised that no one have seen it before. 

Can you send more detailed info on the sample, particles, etc.

Thanks,

	Pelle


On May 13, 2014, at 12:41 PM, Sho Uemura wrote:

> Can look. Can you make available the LCIO file output by the readout 
> simulation?
> 
> On Tue, 13 May 2014, Chad Civello wrote:
> 
>> Hello All,
>> 
>> I am wondering if anyone is familiar with a reconstruction error that I am
>> running into. When attempting to run reconstruction with the
>> HPS2014OfflineTruthRecon.lcsim steering file, the process quits with an
>> error caused by finding a negative value of the variable "t". Upon further
>> investigation, it seems that a negative "t" will cause an imaginary path
>> length of the track, calculated in WTrack.java. The physics behind
>> calculating t is beyond me, involving combinations of a momentum vector, a
>> magnetic field unit vector, and a unit vector of a plane. I am able to step
>> through 590 events before this error occurs, so it seems to be something
>> with this individual event that is stopping reconstruction from continuing.
>> 
>> The file being run through reconstruction is created from running an event
>> file in SLIC with the HPS-Proposal2014-v5-6pt6 detector, and then passing
>> this file through readout simulation with the HPS2014ReadoutNoPileup.lcsim.
>> The output error is listed below.
>> 
>> As a test on the steering file and drivers, I ran a smaller input file
>> through the same reconstruction without an error. However, out of 165
>> triggered events, I am only seeing 14 tracks. Is there a reason that so few
>> tracks would be found? Thank you for the help.
>> 
>> 
>> Regards,
>> 
>> Chad Civello
>> University of New Hampshire
>> 
>> 
>>>> Event 585
>>>> Event 586
>>>> Event 587
>>>> Event 588
>>>> Event 589
>>>> Event 590
>> getPathLengthToPlaneApprox ERROR t is negative (-0.09475479432494227)!
>> p 0.30696444517303073 rho -0.0014649536585467351 a -4.4968868700000003E-4
>> A -3.2568853514089034E-4 B 0.8943517247214046 C -686.7142264081292
>> track params: 0.2785713187164182, -0.12804764158077803,
>> -0.01513249730159967, 0.30696444517303073, 16.49545255281126,
>> 35.88633038244529, 0.656055763097405,
>> xp [      702.45,      71.390,     -27.331]
>> eta [     0.99953,    0.030515,      0.0000]
>> h [      0.0000,      0.0000,     -1.0000]
>> 
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