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UserFunction1D v1¶

Summary ¶

Fits a histogram from a workspace to a user defined function.

Properties ¶

Name	Direction	Type	Default	Description
InputWorkspace	Input	MatrixWorkspace	Mandatory	Name of the input Workspace
WorkspaceIndex	Input	number	0	The Workspace to fit, uses the workspace numbering of the spectra (default 0)
StartX	Input	number	Optional	A value of x in, or on the low x boundary of, the first bin to include in the fit (default lowest value of x)
EndX	Input	number	Optional	A value in, or on the high x boundary of, the last bin the fitting range (default the highest value of x)
Fix	Input	string		A list of comma separated parameter names which should be fixed in the fit
MaxIterations	Input	number	500	Stop after this number of iterations if a good fit is not found
OutputStatus	Output	string
OutputChi2overDoF	Output	number
Function	Input	string	Mandatory	The fit function
InitialParameters	Input	string		The comma separated list of initial values of the fit parameters in the form varName=value
Output	Input	string		If not empty OutputParameters TableWorksace and OutputWorkspace will be created.

This algorithm fits a spectrum to a user defined function. The function is supplied to the algorithm as a text string. The function here is a mathematical expression using numbers, variable names and internal function names. Symbols ‘+’, ‘-’, ‘*’, ‘/’, and ‘^’ can be used for arithmetic operations. Names can contain only letters, digits, and the underscore symbol ‘_’. The internal functions are:

Name	Argc.	Explanation
sin	1	sine function
cos	1	cosine function
tan	1	tangens function
asin	1	arcus sine function
acos	1	arcus cosine function
atan	1	arcus tangens function
sinh	1	hyperbolic sine function
cosh	1	hyperbolic cosine
tanh	1	hyperbolic tangens function
asinh	1	hyperbolic arcus sine function
acosh	1	hyperbolic arcus tangens function
atanh	1	hyperbolic arcur tangens function
log2	1	logarithm to the base 2
log10	1	logarithm to the base 10
log	1	logarithm to the base 10
ln	1	logarithm to base e (2.71828…)
exp	1	e raised to the power of x
sqrt	1	square root of a value
sign	1	sign function -1 if x<0; 1 if x>0
rint	1	round to nearest integer
abs	1	absolute value
if	3	if … then … else …
min	var.	min of all arguments
max	var.	max of all arguments
sum	var.	sum of all arguments
avg	var.	mean value of all arguments

An example of Function property is “a + b*x + c*x^2”. Variable x is used to represent the values of the X-vector of the input spectrum. All other variable names are treated as fitting parameters. A parameter can be given an initial value in the InitialParameters property. For example, “b=1, c=0.2”. The order in which the variables are listed is not important. If a variable is not given a value, it is initialized with 0.0. If some of the parameters should be fixed in the fit list them in the Fix property in any order, e.g. “a,c”.

The resulting parameters are returned in a TableWorkspace set in OutputParameters property. Also for displaying purposes OutputWorkspace is returned. It contains the initial spectrum, the fitted spectrum and their difference.