Ticket #2599 (closed: fixed)
Data going negative after subtracting background, different from collette
Reported by: | Nick Draper | Owned by: | Steve Williams |
---|---|---|---|
Priority: | critical | Milestone: | Iteration 28 |
Component: | Mantid | Keywords: | |
Cc: | Blocked By: | ||
Blocking: | Tester: | Anders Markvardsen |
Description
Reported by Ann Terry:
Just seeing some differences in the output from Mantid compared to Colette. The data in Mantid appears to go negative upon subtracting a background whereas in Colette it is still positive. Sarah and myself have had a look and can’t spot any differences in bin size, q range etc. One guess from Sarah was if it could be due to the wavelength problem Richard highlighted since it is the data at high q which is going negative.
This may need some more input from Richard Heenan
Is this right and is there a solution? For now, users are working with Colette.
Change History
comment:5 Changed 10 years ago by Steve Williams
- Status changed from accepted to verify
- Resolution set to fixed
comment:6 Changed 10 years ago by Steve Williams
- Status changed from verify to reopened
- Resolution fixed deleted
comment:8 Changed 10 years ago by Steve Williams
- Status changed from reopened to accepted
It appears to be fixed From Richard
The background run on the attached, run 61400 has extra large “flat background†in its M2 detector. Having fixed a bug results are now close enough to COLETTE for this run – I’m not expecting them to be identical at small Q as the methods are slightly different and the small Q data is very sensitive to the flat background subtraction under M2.
comment:9 Changed 10 years ago by Steve Williams
- Status changed from accepted to verify
- Resolution set to fixed
comment:10 Changed 9 years ago by Anders Markvardsen
- Status changed from verify to verifying
- Tester set to Anders Markvardsen
comment:11 Changed 9 years ago by Anders Markvardsen
- Status changed from verifying to closed
Looks like in the right direction and Richard is happy. There is a litte bit of negative values but judged to be within errorbars.
Note that hile testing this ticket finds that the following sequence of steps crashes MantidPlot:
- Enter the numbers above in the example Steve provide
- Mask from SVN
- Load data
- Tick 'Plot Result'
- Click the '2D reduce' button
The error message which comes up says 'vector<T> too long'.
Investigating this further we found this appears to be related to log plotting set in preferences along the y-axis
comment:12 Changed 5 years ago by Stuart Campbell
This ticket has been transferred to github issue 3446
This from Richard Heenan
In the ISIS SANS GUI the instrument should be set to LOQ and the emails above typed into its boxes on the first page. When you click Load and then Reduce1D the data shouldn't be more negative than Colette's (i.e. > -0.12)