[Halld-offline] Reconstruction results not consistent

[Kei Moriya]

Hi Will,

Your problem of getting different results every time
you run the program reminds me of a bug I ran into with
genr8 related to random numbers.

If it is the case that you are using random numbers in
your code, it could be that you are setting a different seed
for the random number every time you run.

This could happen for example if you are:
1.  setting the seed with the current time,
     (as genr8 used to)
or,
2. for example, in the function
DKinematicData::smearMCThrownMomentum()
a random seed is set by
rnd.SetSeed((unsigned int)1000 * m_momentum.X());
In this case, depending on whether the momentum
is 0.50044 or 0.50045, you could get a different
seed just on some roundoff error, leading to
possibly a change in the reconstruction.

Have you checked if you have any random numbers?
I'm not sure this has to your problem, but I hope
it helps.

	Kei

(6/29/11 10:35 AM), Beni Zihlmann wrote:
> Hi Will, David,
> I duplicated what you see. I look for each event how many photons are reconstructed. the
> result is
> shown in the two attached files. The diff_sidebyside.dat file shows for each event the
> number of
> reconstructed photons on the left for the first reconstruction on the right for the second
> reconstruction.
> the diff.dat file contains only those event where a difference is found. This should help
> for further
> debuging.
>
> cheers,
> Beni
>
>> Hi,
>> I noticed recently that I've been getting different results when running reconstruction
>> multiple times on the same file. It seems like that for a small number of events, the
>> number of particles reconstructed varies. I think this problem will occur with any
>> input, but I've uploaded one particular hddm file where I've seen the problem
>> (http://www-meg.phys.cmu.edu/wilevine/hdgeant_smeared.hddm ). I think the simplest way
>> to see the problem is to run the reconstruction with the phys_tree plugin twice (i.e.
>> hd_root -PPLUGINS=phys_tree hdgeant_smeared.hddm -o output.1.root
>> hd_root -PPLUGINS=phys_tree hdgeant_smeared.hddm -o output.2.root
>> ) and compare the output. In particular, differences should be seen in the Npip,
>> Nphoton, etc. histograms.
>>
>> For the record I'm using svn revision 7974 and the problem seems to occur in both SIMD
>> and non-SIMD builds.
>>
>> If anyone can confirm or diagnose this issue, that would be helpful.
>>
>> Will
>>
>>
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>
>
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