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SofQWNormalisedPolygon v1

Summary

Calculate the intensity as a function of momentum transfer and energy.

See Also

SofQW, SofQWPolygon, Rebin2D

This algorithm is also known as: SofQW3

Properties

Name

Direction

Type

Default

Description

InputWorkspace

Input

MatrixWorkspace

Mandatory

Reduced data in units of energy transfer DeltaE. The workspace must contain histogram data and have common bins across all spectra.

OutputWorkspace

Output

MatrixWorkspace

Mandatory

The name to use for the q-omega workspace.

QAxisBinning

Input

dbl list

Mandatory

The bin parameters to use for the q axis (in the format used by the Rebin v1 algorithm).

EMode

Input

string

Mandatory

The energy transfer analysis mode (Direct/Indirect). Allowed values: [‘Direct’, ‘Indirect’]

EFixed

Input

number

0

The value of fixed energy: \(E_i\) (EMode=Direct) or \(E_f\) (EMode=Indirect) (meV). Must be set here if not available in the instrument definition.

ReplaceNaNs

Input

boolean

False

If true, all NaN values in the output workspace are replaced using the ReplaceSpecialValues algorithm.

EAxisBinning

Input

dbl list

The bin parameters to use for the E axis (optional, in the format used by the Rebin v1 algorithm).

DetectorTwoThetaRanges

Input

TableWorkspace

A table workspace use by SofQWNormalisedPolygon containing a ‘Detector ID’ column as well as ‘Min two theta’ and ‘Max two theta’ columns listing the detector’s min and max scattering angles in radians.

Description

Converts a 2D workspace from units of spectrum number/energy transfer to the intensity as a function of momentum transfer \(Q\) and energy transfer \(\Delta E\).

The details of the Normalised Polygon technique for rebinning are given in FractionalRebinning.

The algorithm operates in non-PSD mode by default. This means that the scattering angle \(2\theta\) range covered by a detector is calculated for each detector individually. For grouped detectors, it is the minimum and maximum \(2\theta\) of all detectors in the group. The computation is accurate for simple detector shapes (cylinder, cuboid); for other shapes a more rough method is used. It is possible to provide precalculated per-detector \(2\theta\) values using the DetectorTwoThetaRanges input property.

PSD mode will determine the detector \(2\theta\) ranges from the instrument geometry. This mode is activated by placing the following named parameter in the instrument definition file: detector-neighbour-offset. The integer value of this parameter should be the number of pixels that separates two pixels at the same vertical position in adjacent tubes.

See SofQWCentre v1 for centre-point binning or SofQWPolygon v1 for simpler and less precise but faster binning strategies. The speed-up is from ignoring the azimuthal positions of the detectors (as for the non-PSD mode in this algorithm) but in addition, SofQWPolygon v1 treats all detectors as being the same, and characterised by a single width in scattering angle. Thereafter, it weights the signal and error by the fractional overlap, similarly to that shown in the first figure above, but then discards the summed weights, producing a Workspace2D rather than a RebinnedOutput workspace.

Usage

Example - simple transformation of inelastic workspace:

# create sample inelastic workspace for MARI instrument containing 1 at all spectra
ws=CreateSimulationWorkspace(Instrument='MAR',BinParams='-10,1,10')
# convert workspace into Matrix workspace with Q-dE coordinates
ws=SofQWNormalisedPolygon(InputWorkspace=ws,QAxisBinning='-3,0.1,3',Emode='Direct',EFixed=12)

print("The converted X-Y values are:")
Xrow=ws.readX(59);
Yrow=ws.readY(59);
line1= " ".join('! {0:>6.2f} {1:>6.2f} '.format(Xrow[i],Yrow[i]) for i in range(0,10))
print(line1 + " !")
line2= " ".join('! {0:>6.2f} {1:>6.2f} '.format(Xrow[i],Yrow[i]) for i in range(10,20))
print(line2 + " !")
print('! {0:>6.2f} ------- !'.format(Xrow[20]))

Output:

The converted X-Y values are:
! -10.00   1.00  !  -9.00   1.00  !  -8.00   1.00  !  -7.00   1.00  !  -6.00   1.00  !  -5.00   1.00  !  -4.00   1.00  !  -3.00   1.00  !  -2.00   1.00  !  -1.00   1.00  !
!   0.00   1.00  !   1.00   1.00  !   2.00   1.00  !   3.00   1.00  !   4.00   1.00  !   5.00   1.00  !   6.00   1.00  !   7.00   1.00  !   8.00   1.00  !   9.00   1.00  !
!  10.00 ------- !

Categories: AlgorithmIndex | Inelastic\SofQW

Source

C++ header: SofQWNormalisedPolygon.h

C++ source: SofQWNormalisedPolygon.cpp