Add polarizer efficiency algorithm

[jclarkeSTFC]

New algorithm to calculate the supermirror polarizer efficiency using a group workspace with 4 runs for the 4 spin combinations, plus the efficiency of the analyser cell, calculated previously. This is part of the polarized SANS epic.

Output can either be to a workspace, a file, or both.

Fixes #36139

Summary of work

• Added algorithm
• Added tests
• Added doc page

Further detail of work

Calculates how the efficiency of a polarizer varies with wavelength. The ordering of the workspaces in InputWorkspace is taken from the SpinStates parameter, and the analyser efficiency, e_cell, is given by AnalyserEfficiency.

The polarization of the polarizer, P_SM, is given by

Since the efficiency, e_SM , is given by (1 + P_SM)/2, we have that

To test:

This will generate a simple example:

wsPara = CreateSampleWorkspace('Histogram', Function='User Defined', UserDefinedFunction='name=UserFunction,Formula=0.5*exp(-0.0733*12*x*(1-0.9))',XUnit='Wavelength', xMin='1',XMax='8', BinWidth='1')
wsPara1 = CloneWorkspace(wsPara)
wsAnti = CreateSampleWorkspace('Histogram', Function='User Defined', UserDefinedFunction='name=UserFunction,Formula=0.5*exp(-0.0733*12*x*(1+0.9))',XUnit='Wavelength', xMin='1',XMax='8', BinWidth='1')
wsAnti1 = CloneWorkspace(wsAnti)

grp = GroupWorkspaces([wsPara,wsAnti,wsPara1,wsAnti1])
eCell = CreateSampleWorkspace('Histogram', Function='User Defined', UserDefinedFunction='name=UserFunction,Formula=(1 + tanh(0.0733 * 12 * x * 0.2))/2',XUnit='Wavelength', xMin='1',XMax='16', BinWidth='1')

psm = PolarizerEfficiency(grp, eCell)
print("Polarizer efficiency at a wavelength of " + str(mtd['psm'].dataX(0)[3]) + " Å is " + str(mtd['psm'].dataY(0)[3]))

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[github-actions[bot]]

:wave: Hi, @jclarkeSTFC,

Conflicts have been detected against the base branch. Please rebase your branch against the base branch.

[jclarkeSTFC]

Code Review:

* Have a few code notes, but it's looking good.

Functional testing:

* Working well from both the script and the algorithm dialog. Tried a few different bad inputs and it handled them well.

* The 1st column of the output data from the script you provided seems to provide an efficiency value of `-1.108...`. I was under the impression efficiencies should always be between 0 and 1, so I just want to check if that's expected or if I've not got confused about something.

Docs:

* Look great! Thanks for including the maths for both the polarisation and the efficiency.

Thanks, I think I've changed all the things you spotted, and I've updated to the new equation.

[github-actions[bot]]

:wave: Hi, @jclarkeSTFC,

Conflicts have been detected against the base branch. Please rebase your branch against the base branch.

[rbauststfc]

Just making a note that because we'll now be targeting 6.11 for this change, we'll need to rebase and move the release note to the appropriate 6.11 folder.

[cailafinn]

Re-created the PR here as I can't push to this branch:

• https://github.com/mantidproject/mantid/pull/37616