Ticket #4262 (closed: fixed)
SmoothNeighbours: incorrect errors?
Reported by: | Janik Zikovsky | Owned by: | Janik Zikovsky |
---|---|---|---|
Priority: | minor | Milestone: | Release 2.0 |
Component: | Mantid | Keywords: | |
Cc: | owen.arnold@… | Blocked By: | |
Blocking: | Tester: | Wenduo Zhou |
Description
Hi Janik,
I've noticed that in the processing of errors in SmoothNeighbours, for MatrixWorkspaces, you square the error, then multiply by the weight, then take the sqrt of the error. Pascal is complaining that the weights aren't coming out right on SmoothNeighbours, but the only dubious thing that I see done is this multiplication by the error2. Why are we applying the weights to the error2?
Thanks, Owen.
Change History
comment:2 Changed 9 years ago by Janik Zikovsky
I'm not sure what Pascal sees incorrect in the weights, but the errors were indeed incorrect as I describe above.
comment:4 Changed 9 years ago by Owen Arnold
I tested this out and it seems to work. Code changes look sensible too.
comment:5 Changed 9 years ago by Janik Zikovsky
- Status changed from accepted to verify
- Resolution set to fixed
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Refs #4262: Fixing error calculation for SmoothNeighbours
As per proper error propagation formulae, when multiplying by an exactly known value (the weight), the error squared is scaled by the weight squared. Test modified to reflect this: the output workspace has lower errors since each pixel has improved statistics.