3.8

SofQW v1

../_images/SofQW-v1_dlg.png

SofQW dialog.

Summary

Computes S(Q,w) using a either centre point or parallel-piped rebinning. The output from each method is: CentrePoint - centre-point rebin that takes no account of pixel curvature or area overlap

Polygon - parallel-piped rebin, outputting a weighted-sum of overlapping polygons

NormalisedPolygon - parallel-piped rebin, outputting a weighted-sum of overlapping polygons normalised by the fractional area of each overlap

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.
Method Input string Centre Defines the method used to compute the output. Allowed values: [‘Centre’, ‘Polygon’, ‘NormalisedPolygon’]

Description

This algorithm is for use by inelastic instruments and takes as its input a workspace where the data’s been reduced to be in units of energy transfer against spectrum number (which can be seen as equivalent to angle, with the angle being taken from the detector(s) to which the spectrum pertains).

This algorithm can operate in one of three modes. Each mode simply runs a different algorithm to perform the computation:

  • Centre: performs a basic centre-point rebinning, see SofQWCentre v1
  • Polygon: performs a parallel-piped rebin, taking into account the curvature of the output bins see SofQWPolygon v1
  • NormalisedPolygon: performs the same rebin as Polygon but the output bins normalised by the contributing overlap area see SofQWNormalisedPolygon v1

The energy binning will not be changed by this algorithm, so the input workspace should already have the desired bins (though this axis can be rebinned afterwards if desired). The EMode and EFixed parameters are used for the calculation of Q.

If the input workspace is a distribution (i.e. counts/meV ) then the output workspace will similarly be divided by the bin width in both directions (i.e. will contain counts/meV/(1/Angstrom) ).

Usage

Example - simple transformation of inelastic workspace:

# create sample inelastic workspace for MARI instrument containing 1 at all spectra values
ws=CreateSimulationWorkspace(Instrument='MAR',BinParams='-10,1,10')
# convert workspace into MD workspace
ws=SofQW(InputWorkspace=ws,QAxisBinning='-3,0.1,3',Emode='Direct',EFixed=12)

print "The converted X values are:"
print ws.readX(59)[0:10]
print ws.readX(59)[10:21]

print "The converted Y values are:"
print ws.readY(59)[0:10]
print ws.readY(59)[10:21]

Output:

The converted X values are:
[-10.  -9.  -8.  -7.  -6.  -5.  -4.  -3.  -2.  -1.]
[  0.   1.   2.   3.   4.   5.   6.   7.   8.   9.  10.]
The converted Y values are:
[ 12.  18.  18.  18.  18.  21.  18.  18.  21.  12.]
[ 18.  21.  24.  24.  24.  21.  24.  33.  39.  45.]

Categories: Algorithms | Inelastic\SofQW

Source

C++ source: SofQW.cpp

C++ header: SofQW.h