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# QENSFitSequential v1¶

## Summary¶

Performs a sequential fit for QENS data

## Properties¶

Name

Direction

Type

Default

Description

InputWorkspace

Input

MatrixWorkspace

The input workspace for the fit. This property will be ignored if ‘Input’ is provided.

SpecMin

Input

number

0

The first spectrum to be used in the fit. Spectra values can not be negative. This property will be ignored if ‘Input’ is provided.

SpecMax

Input

number

0

The final spectrum to be used in the fit. Spectra values can not be negative. This property will be ignored if ‘Input’ is provided.

Input

Input

string

A list of sources of data to fit. Sources can be either workspace names or file names followed optionally by a list of spectra/workspace-indices or values using the notation described in the description section of the help page.

ResultXAxisUnit

Input

string

MomentumTransfer

The unit to assign to the X Axis of the result workspace, defaults to MomentumTransfer. Allowed values: [‘AtomicDistance’, ‘Degrees’, ‘DeltaE’, ‘DeltaE_inFrequency’, ‘DeltaE_inWavenumber’, ‘dSpacing’, ‘dSpacingPerpendicular’, ‘Empty’, ‘Energy’, ‘Energy_inWavenumber’, ‘Label’, ‘Momentum’, ‘MomentumTransfer’, ‘Phi’, ‘QSquared’, ‘SpinEchoLength’, ‘SpinEchoTime’, ‘Temperature’, ‘Time’, ‘TOF’, ‘Wavelength’, ‘’]

OutputWorkspace

Output

WorkspaceGroup

Mandatory

The output result workspace(s)

OutputParameterWorkspace

Output

TableWorkspace

The output parameter workspace

OutputWorkspaceGroup

Output

WorkspaceGroup

The output group workspace

Function

InOut

Function

Mandatory

The fitting function, common for all workspaces in the input.

LogName

Input

string

axis-1

Name of the log value to plot the parameters against. Default: use spectra numbers.

StartX

Input

dbl list

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

dbl list

A value in, or on the high x boundary of, the last bin the fitting range (default the highest value of x)

PassWSIndexToFunction

Input

boolean

False

For each spectrum in Input pass its workspace index to all functions thathave attribute WorkspaceIndex.

Minimizer

Input

string

Levenberg-Marquardt

Minimizer to use for fitting. Minimizers available are ‘Levenberg-Marquardt’, ‘Simplex’, ‘FABADA’, ‘Conjugate gradient (Fletcher-Reeves imp.)’, ‘Conjugate gradient (Polak-Ribiere imp.)’ and ‘BFGS’

CostFunction

InOut

string

Least squares

Cost functions to use for fitting. Cost functions available are ‘Least squares’ and ‘Ignore positive peaks’. Allowed values: [‘Least squares’, ‘Poisson’, ‘Rwp’, ‘Unweighted least squares’]

MaxIterations

Input

number

500

Stop after this number of iterations if a good fit is not found

Input

number

0

A value of the peak radius the peak functions should use. A peak radius defines an interval on the x axis around the centre of the peak where its values are calculated. Values outside the interval are not calculated and assumed zeros.Numerically the radius is a whole number of peak widths (FWHM) that fit into the interval on each side from the centre. The default value of 0 means the whole x axis.

ExtractMembers

Input

boolean

False

If true, then each member of the fit will be extracted, into their own workspace. These workspaces will have a histogram for each spectrum (Q-value) and will be grouped.

OutputCompositeMembers

Input

boolean

False

If true and CreateOutput is true then the value of each member of a Composite Function is also output.

ConvolveMembers

Input

boolean

False

If true and OutputCompositeMembers is true members of any Convolution are output convolved with corresponding resolution

EvaluationType

Input

string

CentrePoint

The way the function is evaluated: CentrePoint or Histogram. Allowed values: [‘CentrePoint’, ‘Histogram’]

FitType

Input

string

Sequential

Defines the way of setting initial values. If set to Sequential every next fit starts with parameters returned by the previous fit. If set to Individual each fit starts with the same initial values defined in the Function property. Allowed values: [Sequential, Individual]. Allowed values: [‘Sequential’, ‘Individual’]

Exclude

Input

dbl list

A list of pairs of real numbers, defining the regions to exclude from the fit.

ExcludeMultiple

Input

str list

A list of Exclusion ranges, defining the regions to exclude from the fit for each spectra. Must have the same number of sets as the number of the spectra.

IgnoreInvalidData

Input

boolean

False

Flag to ignore infinities, NaNs and data with zero errors.

OutputFitStatus

Input

boolean

False

Flag to output fit status information, which consists of the fit OutputStatus and the OutputChiSquared

## Description¶

An algorithm used for fitting QENS-data sequentially and formatting the output. Uses the PlotPeakByLogValue algorithm to perform the sequential fit.

The string format expected by the “Input” property of this algorithm is outlined in PlotPeakByLogValue.

## Usage¶

Example - QENSFitSequential

# Load sample and resolution files

# Set up algorithm parameters
function = """name=LinearBackground,A0=0,A1=0,ties=(A0=0.000000,A1=0.0);
(composite=Convolution,FixResolution=true,NumDeriv=true;
name=Resolution,Workspace=resolution,WorkspaceIndex=0;
name=Lorentzian,Amplitude=1,PeakCentre=0,FWHM=0.0175)"""
startX = -0.547608
endX = 0.543217
convolve = True  # Convolve the fitted model components with the resolution
minimizer = "Levenberg-Marquardt"
maxIt = 500

# Run algorithm
result, params, fit_group = QENSFitSequential(InputWorkspace=sample,
Function=function,
PassWSIndexToFunction=True,
StartX=startX, EndX=endX,
ConvolveMembers=convolve,
Minimizer=minimizer, MaxIterations=maxIt)

# The QENSFitSequential algorithm can take an optional OutputFitStatus flag, to output the Chi squared and fit status
# of each fit
result, params, fit_group, fit_status, chi2 = QENSFitSequential(InputWorkspace=sample,
Function=function,
PassWSIndexToFunction=True,
StartX=startX, EndX=endX,
ConvolveMembers=convolve,
Minimizer=minimizer, MaxIterations=maxIt,
OutputFitStatus=True)


Categories: AlgorithmIndex | Workflow\MIDAS