Getting EFixed from ExperimentInfo

General
1

I’m trying to read the EFixed value from a workspace without success. This seems to need an ExperimentInfo, but I can’t work out how to get a handle on it.

For spectrum info I can use:

ws = mtd['iris88490_graphite002_red']
spec_info = ws.spectrumInfo()
twoth = [i.twoTheta for i in spec_info]
print (twoth)

Although it is possible to use ws.getExperimentInfo() on an event workspace, this is not possible on a workspace 2D.

I would imagine I should be able to use something like:

ws = mtd['iris88490_graphite002_red']
exp_info = ws.experimentInfo()
ef = exp.info.Efixed
print (ef)

How can I read EFixed relating to a 2D Workspace?

2

You should simply be able to run ws.getEFixed(detid) where detid is the DetectorID.

3

Thanks Daniel,

that will work for me in a hacky way for my script. I’m trying to get it to work with different detector groupings and I can’t guarantee that a given detector is present or know which spectrum number it is associated with. Is there a way to get a DetectorID from a spectrum number or EFixed for a spectrum?

4

You could also use ws.getInstrument().getNumberParameter(‘EFixed’)[0]
Efixed for indirect geometry is the d-spacing of the analyser. Why would this depend on detectorID?

5

Thanks Spencer, that makes sense.

The EFixed would not depend on DetectorID. I would normally go for spectrum[0], as that is present independent of how reduction is done. If I went for ws.getEFixed(det3), but the detector was not involved in the reduction, then it would fail.

6

Thank you for your input Spencer!

On the workspace I’ve tested on, your command doesn’t work for me. The following worked: energy = ws.getInstrument().getDetector(3).getNumberParameter('Efixed')[0]
where the DetectorID was 3.

7

Ian, since you know what spectrum number you want to use, then you could try this:

ws = mtd['IRIS']
detID = ws.getSpectrum(0).getDetectorIDs()
ei_val = ws.getInstrument().getDetector(detID[0]).getNumberParameter('Efixed')[0]
print(ei_val)

so the detectorIDs relevant to your spectrum are extracted and one of them is then used for the EFixed value. I get that it’s annoying that you have to reference the DetectorID when it’s the same value for all, at least in this case.

8

Reading around a bit more (I’m very much still learning python & Mantid), it seems that there should be a better way of what I’m trying to do.

What I really want to do is to set an instrument (IRIS or OSIRIS), then the instrument configuration (analyser & reflection), then read some of the parameter values from the IDF and parameters file.

In pseudocode:

my_inst_setup = loadInstrument(instrument = 'IRIS', analyser = 'graphite', reflection = '002' )
ef = my_inst_setup.getEfixed()

Is there a way to do this without parsing the xml of the IDF and components files?

9

All this is done in the indirect scripts. There are lots of routines in the scripts IndirectCommon.py & IndirectNeutron.py which you can find in the ManidInstall scripts/inelastic directory

10

The analyser/reflection is in the Instrument Parameter File so you can just LoadInstrumentParameter

11

You should be able to run:

from IndirectCommon import getEfixed
ws= mtd['irs26173_graphite002_red']
print( getEfixed(ws) )

The IndirectCommon.py file: mantid/IndirectCommon.py at master · mantidproject/mantid · GitHub

12

LoadInxAscii.py (9.2 KB)
Here’s a worked example of creating a workspace using instrument parameters etc which I use for dealing with ascii files.

13

Thanks both, that’s great.