Bug #2804

Inconsistencies between branch 2713-variability-tool and devel branch

Added by Bonnefoy Simon about 5 years ago. Updated about 5 years ago.

Status:ClosedStart date:01/24/2019
Priority:NormalDue date:
Assigned To:Bonnefoy Simon% Done:

100%

Category:-
Target version:1.6.0
Duration:

Description

The branch 2713-variability-tool has been merged with the devel branch.
However, it seems that there are some inconsistencies in the results between both branches for the ctfindvar tool.
The devel branches exhibits variability with significance above 5 sigma in regions where no variability is expected (from simulation).

Furthermore, it seems that running ctfindvar several times changes the results in the map.fits file.

The dataset used is a simulation from ctobsim, with temporal dependency in the signal.

Below is the lightcurve from branch 2713

Below are shown different lightcurve from the devel branch.
Each plots represents the output of one instance of ctfindvar on the same dataset.
We can see that there are discrepencies
between the two analysis.


ctfindvar_devel_variability2.png (186 KB) Bonnefoy Simon, 01/24/2019 11:16 AM

ctfindvar_devel_variability1.png (215 KB) Bonnefoy Simon, 01/24/2019 11:20 AM

ctfindvar_2713_variability.png (211 KB) Bonnefoy Simon, 01/24/2019 11:20 AM

Ctfindvar_devel_variability2 Ctfindvar_devel_variability1 Ctfindvar_2713_variability

Recurrence

No recurrence.

History

#1 Updated by Bonnefoy Simon about 5 years ago

  • File deleted (screenshot_3_1548324281_ctfindvar_2713_variability.png)

#3 Updated by Bonnefoy Simon about 5 years ago

  • File deleted (screenshot_2_1548324274_ctfindvar_devel_variability1.png)

#4 Updated by Bonnefoy Simon about 5 years ago

  • File deleted (screenshot_1_1548324258_ctfindvar_2713_variability.png)

#6 Updated by Bonnefoy Simon about 5 years ago

It seems that the bug comes from the multi process that is started on line 767 of ctfindvar.cpp,
just before looping over all the pixels in the cube.
Commenting the line
//#pragma omp parallel for
seems to do the job.

#7 Updated by Knödlseder Jürgen about 5 years ago

  • Status changed from New to In Progress
  • Target version set to 1.6.0
  • % Done changed from 0 to 10

I looked into the code I could not find anything strange going on. Have you tested multi-processing before, and did this bug only occur after I integrated the code?

#8 Updated by Knödlseder Jürgen about 5 years ago

You may add additional critical zones to the code in order to identify which of the instructions creates at the end a problem (if everything within the for loop is critical no multi-processing should happen, hence the bug should also disappear).

#9 Updated by Bonnefoy Simon about 5 years ago

Yes, we tested multi-processing before and it was working well.
It seems that the problems come from the line 777

GNdarray pixSig = get_variability_sig(ipix);

This function has been modified when merged to the devel branch.
Before, the GNdarray in which the significance is stored for each pixel was given as an argument. Now it is created in the function.
I don’t know whether this might have an impact when multi-processing.

In the ctfindvar::analyse_cube, declaring the GNdarray pixSig at the beginning of the analyse_cube method, and adding a pragma omp critical before the get_variability_sig seems to be working fine.

#10 Updated by Knödlseder Jürgen about 5 years ago

Maybe I have misunderstood what get_variability_sig() is doing. I thought that get_variability_sig() always returns an updated GNdarray, but looking again at the old code it seems that there can be conditions where the old values are kept:

            // The GTI is discared from bckg calculation and not checked again.
            if (!accepted_bin_bckg_vector[i]) {
                continue;
            } 
            // Check if bin fails minoff check or no observations overlap it
            else if (m_counts(pix_number, i) < m_minoff || alpha_vector[i] == 0) {
                accepted_bin_bckg_vector[i] = false;
                continue;
            }

If this is indeed the intention I would suggest to put back GNdarray as a method argument. In that case I suppose that no pragma is needed.

#11 Updated by Bonnefoy Simon about 5 years ago

OK, it seems that the problem comes from the ctfindvar_get_alphas method.
There was, in the branch 2713, a
#omp pragma critical(ctfindvar_get_alphas)
just before the
alphas[j] += exposure * bkg->rate_ebin(instdir, m_emin, m_emax);
line 1127.
This critical is not in the devel branch.
It seems that the problem is solved by just adding a critical here.

#12 Updated by Knödlseder Jürgen about 5 years ago

  • Status changed from In Progress to Feedback
  • % Done changed from 10 to 100

I added the line that you suggested to the code.

While writing up the code description for the H.E.S.S. paper, I also recognised that in ctfindvar::get_variability_sig the exclusion of bins with m_counts(ipix, i) < m_minoff was done in the iterative loop, which means that the bins were not necessarily excluded for the background computation. If I understood correctly your intention, the bins have to be excluded before the iterative loop is entered. I therefore modified the code as follows:

GNdarray ctfindvar::get_variability_sig(const int& ipix)
{
    // Initialise result
    GNdarray sig_histogram(m_gti.size());

    // Initialise vectors
    std::vector<bool> accepted_bin_bckg_vector(m_gti.size(), true);

    // Get alpha values for specified pixel
    std::vector<double> alphas = get_alphas(ipix);

    // Exclude all bins from the background estimate for which the
    // number of events is below "minoff" or for which alpha is zero
    for (int i = 0; i < m_gti.size(); ++i) {
        if (m_counts(ipix, i) < m_minoff || alphas[i] == 0.0) {
            accepted_bin_bckg_vector[i] = false;
        }
    }

    // Loop over pixels until all background pixels are removed
    bool background_validated = false;
    while (background_validated == false) {

        // Signal that background was validated
        background_validated = true;

Can you please let me know if this is correct, and if the code now works for you as expected?

I integrated the code in the devel branch.

#13 Updated by Bonnefoy Simon about 5 years ago

Yes, you are right, it is better to discard the GTIs with m_counts(ipix, i) < m_minoff before entering the while,
so they don’t participate in any way to the background calculation.
I have tested the code. Everything seems to be working well from my side.
Thank you very much!

#14 Updated by Knödlseder Jürgen about 5 years ago

  • Status changed from Feedback to Closed

Great, I close then the issue.

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