SofQW v1¶

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: (EMode=Direct) or (EMode=Indirect) (meV). Must be set here if not available in the instrument definition.
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 .

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

Source¶

C++ source: SofQW.cpp

C++ header: SofQW.h