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ConvertToDiffractionMDWorkspace v3¶
Summary¶
Create a MDEventWorkspace with events in reciprocal space (Qx, Qy, Qz) for an elastic diffraction experiment.
See Also¶
Properties¶
Name 
Direction 
Type 
Default 
Description 

InputWorkspace 
Input 
Mandatory 
An input workspace. 

OutputWorkspace 
Output 
Mandatory 
Name of the output MDEventWorkspace. If the workspace already exists, then the events will be added to it. 

Append 
Input 
boolean 
False 
Append events to the output workspace. The workspace is replaced if unchecked. 
ClearInputWorkspace 
Input 
boolean 
False 
Clearing the events from the input workspace during conversion (to save memory) is not supported by algorithm v2 
OneEventPerBin 
Input 
boolean 
True 
Use the histogram representation (event for event workspaces). One MDEvent will be created for each histogram bin (even empty ones). Warning! This can use significantly more memory! 
OutputDimensions 
Input 
string 
Q (lab frame) 
What will be the dimensions of the output workspace? Q (lab frame): Wavevector change of the lattice in the lab frame. Q (sample frame): Wavevector change of the lattice in the frame of the sample (taking out goniometer rotation). HKL: Use the sample’s UB matrix to convert to crystal’s HKL indices. Allowed values: [‘Q (sample frame)’, ‘Q (lab frame)’, ‘HKL’] 
LorentzCorrection 
Input 
boolean 
False 
Correct the weights of events by multiplying by the Lorentz formula: sin(theta)^2 / lambda^4 
SplitInto 
Input 
int list 
2 
A comma separated list of into how many subgrid elements each dimension should split; or just one to split into the same number for all dimensions. Default 2. 
SplitThreshold 
Input 
number 
1500 
How many events in a box before it should be split. Default 1500. 
MaxRecursionDepth 
Input 
number 
20 
How many levels of box splitting recursion are allowed. The smallest box will have each side length \(l = (extents) / (SplitInto^{MaxRecursionDepth}).\) Default 20. 
MinRecursionDepth 
Input 
number 
1 
Optional. If specified, then all the boxes will be split to this minimum recursion depth. 1 = one level of splitting, etc. Be careful using this since it can quickly create a huge number of boxes = (SplitInto ^ (MinRercursionDepth * NumDimensions)). But setting this property equal to MaxRecursionDepth property is necessary if one wants to generate multiple file based workspaces in order to merge them later 
Extents 
Input 
dbl list 
A comma separated list of min, max for each dimension, specifying the extents of each dimension. Optional, default will use ConvertToMDMinMaxLocal to calculate extents for each dimension. 
Description¶
The algorithm converts from a MatrixWorkspace (in any input units) into a MDWorkspace containing 3D events in reciprocal space.
The calculations apply only to elastic diffraction experiments. The conversion can be done either to Qspace in the lab or sample frame, or to HKL of the crystal.
Version 3 of this algorithm will by default automatically calculate the extents of the MD workspace using the ConvertToMDMinMaxLocal v1 algorithm. Old version of this algorithm (version 2) also still exists which uses the fixed bounds +/ 50. See the ConvertToDiffractionMDWorkspace v2 for details of the old implementation and ConvertToMDMinMaxLocal v1 for information on how extents are now calculated.
Types of Conversion¶
Q (lab frame): this calculates the momentum transfer (kikf) for each event is calculated in the experimental lab frame.
Q (sample frame): the goniometer rotation of the sample is taken out, to give Q in the frame of the sample. See SetGoniometer v1 to specify the goniometer used in the experiment.
HKL: uses the UB matrix (see SetUB v1, FindUBUsingFFT v1 and others) to calculate the HKL Miller indices of each event.
Lorentz Correction¶
If selected, the following Lorentz correction factor is applied on each event by multiplying its weight by L:
\(L = \frac{ sin(\theta)^2 } { \lambda^{4} }\)
Where \(\theta\) is half of the neutron scattering angle (conventionally called \(2\theta\)). \(\lambda\) is the neutron wavelength in Angstroms.
This correction is also done by the AnvredCorrection v1 algorithm, and will be set to false if that algorithm has been run on the input workspace.
Usage
Example  Convert rebinned MARI 2D workspace to 3D MD workspace for further analysis/merging with data at different temperatures :
# create or load event workspace
events = CreateSampleWorkspace(OutputWorkspace='events', WorkspaceType='Event', Function='Multiple Peaks')
# convert to MD workspace
md = ConvertToDiffractionMDWorkspace(InputWorkspace=events, OutputWorkspace='md', OneEventPerBin=False, LorentzCorrection=True, SplitThreshold=150)
# A way to look at these results as a text:
print("Resulting MD workspace has {0} events and {1} dimensions".format(md.getNEvents(),md.getNumDims()))
print("Workspace Type is: {}".format(md.id()))
Output:
Resulting MD workspace has ... events and 3 dimensions
Workspace Type is: MDEventWorkspace<MDEvent,3>
Categories: AlgorithmIndex  MDAlgorithms\Creation
Source¶
C++ header: ConvertToDiffractionMDWorkspace3.h
C++ source: ConvertToDiffractionMDWorkspace3.cpp