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TabulatedFunction

Description

A function which takes its values from a file or a workspace. The values are tabulated as x,y pairs. Liear interpolation is used for points between the tabulated values. The function returns zero for points outside the tabulated values.

The files can be either ascii text files or nexus files. The ascii files must contain two column of real numbers separated by spaces. The first column are the x-values and the second one is for y.

If a nexus file is used its first spectrum provides the data for the function. The same is true for a workspace which must be a MatrixWorkspace.

Attributes (non-fitting parameters)

Name	Type	Default	Description
FileName
Workspace
WorkspaceIndex
X
Y

Properties (fitting parameters)

Name	Default	Description
Scaling	1.0	A scaling factor
Shift	0.0	Shift in the abscissa
XScaling	1.0	Scaling factor in X

Usage

Note

To run these usage examples please first download the usage data, and add these to your path. In Mantid this is done using Manage User Directories.

Example - Fit two structure factors that are shifted and scaled with respect to each other:

ws1=LoadNexus('tabulatedFunctionExample.nxs')

# Clone the workspace by rescaling and shift
ws2=CloneWorkspace(ws1)
ws2=Scale(ws2, Factor=1.34, Operation='Multiply')
ws2=ScaleX(ws2, Factor=0.002, Operation='Add')

# Call the Fit algorithm and perform the fit
myFunc='name=TabulatedFunction,Workspace=ws1,WorkspaceIndex=0,Scaling=1.0,Shift=0.0'
fit_output = Fit(Function=myFunc, InputWorkspace=ws2, Output='fit')
paramTable = fit_output.OutputParameters  # table containing the optimal fit parameters
fitWorkspace = fit_output.OutputWorkspace

print("The fit was: " + fit_output.OutputStatus)
print("Fitted Scaling value is: %.2f" % paramTable.column(1)[0])
print("Fitted Shift value is: %.3f" % abs(paramTable.column(1)[1]))
# fitWorkspace contains the data, the calculated and the difference patterns
print("Number of spectra in fitWorkspace is: " +  str(fitWorkspace.getNumberHistograms()))

Output:

The fit was: success
Fitted Scaling value is: 1.34
Fitted Shift value is: 0.002
Number of spectra in fitWorkspace is: 3

Categories: FitFunctions | General

Source

C++ header: TabulatedFunction.h

C++ source: TabulatedFunction.cpp