6.4

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CrossCorrelate v1

../_images/CrossCorrelate-v1_dlg.png

CrossCorrelate dialog.

Summary

Cross-correlates a range of spectra against one reference spectra in the same workspace.

Properties

Name Direction Type Default Description
InputWorkspace Input MatrixWorkspace Mandatory A 2D workspace with X values of d-spacing
OutputWorkspace Output MatrixWorkspace Mandatory The name of the output workspace
ReferenceSpectra Input number 0 The Workspace Index of the spectra to correlate all other spectra against.
WorkspaceIndexMin Input number 0 The workspace index of the first member of the range of spectra to cross-correlate against.
WorkspaceIndexMax Input number 0 The workspace index of the last member of the range of spectra to cross-correlate against.
XMin Input number 0 The starting point of the region to be cross correlated.
XMax Input number 0 The ending point of the region to be cross correlated.
MaxDSpaceShift Input number Optional Optional float for maximum shift to calculate (in d-spacing)

Description

Compute the cross correlation function for a range of spectra with respect to a reference spectrum.

\[c_{fg}(r) = \frac{1}{\sigma_f \sigma_g} \int (f(x) - \mu_f) (g(x+r)-\mu_g) dx\]

This is use in powder diffraction experiments when trying to estimate the offset of one spectra with respect to another one. The spectra are converted in d-spacing and then interpolate on the X-axis of the reference. The cross correlation function is computed in the range [-N/2,N/2] where N is the number of points.

More details can be found here.

Usage

Example - Crosscorrelate 2 spectra

#Create a workspace with 2 spectra with five bins of width 0.5
ws = CreateSampleWorkspace(BankPixelWidth=1, XUnit='dSpacing', XMax=5, BinWidth=0.5)
ws = ScaleX(InputWorkspace='ws', Factor=0.5, Operation='Add', IndexMin=1, IndexMax=1)
# Run algorithm  CrossCorrelate
OutputWorkspace = CrossCorrelate(InputWorkspace='ws', WorkspaceIndexMax=1, XMin=2, XMax=4)

# Show workspaces
print("AutoCorrelation {}".format(OutputWorkspace.readY(0)))
print("CrossCorrelation {}".format(OutputWorkspace.readY(1)))

AutoCorrelation [-0.01890212  1.         -0.01890212]
CrossCorrelation [-0.68136257  0.16838401  0.45685055]

Categories: AlgorithmIndex | Arithmetic

Source

C++ header: CrossCorrelate.h

C++ source: CrossCorrelate.cpp