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CreateSampleWorkspace v1

Summary

Creates sample workspaces for usage examples and other situations.

See Also

CreateWorkspace

Properties

Name	Direction	Type	Default	Description
OutputWorkspace	Output	MatrixWorkspace	Mandatory	An output workspace.
WorkspaceType	Input	string	Histogram	The type of workspace to create (default: Histogram). Allowed values: [‘Histogram’, ‘Event’]
Function	Input	string	One Peak	Preset options of the data to fill the workspace with. Allowed values: [‘Exp Decay’, ‘Flat background’, ‘Multiple Peaks’, ‘One Peak’, ‘Powder Diffraction’, ‘Quasielastic’, ‘Quasielastic Tunnelling’, ‘User Defined’]
UserDefinedFunction	Input	string		Parameters defining the fitting function and its initial values
XUnit	Input	string	TOF	The unit to assign to the XAxis (default:”TOF”)
XMin	Input	number	0	The minimum X axis value (default:0)
XMax	Input	number	20000	The maximum X axis value (default:20000)
BinWidth	Input	number	200	The bin width of the X axis (default:200)
NumEvents	Input	number	1000	The number of events per detector, this is only used for EventWorkspaces (default:1000)
Random	Input	boolean	False	Whether to randomise the placement of events and data (default:false)
NumScanPoints	Input	number	1	Add a number of time indexed detector scan points to the instrument. The detectors are rotated in 1 degree increments around the sample position in the x-z plane. Minimum (default) is 1 scan point, which gives a non-scanning workspace.
InstrumentName	Input	string	basic_rect
NumBanks	Input	number	2	The Number of banks in the instrument (default:2)
NumMonitors	Input	number	0	The number of monitors in the instrument (default:0)
BankPixelWidth	Input	number	10	The number of pixels in horizontally and vertically in a bank (default:10)
PixelDiameter	Input	number	0.008	Length in meters of one side of a pixel assumed to be square
PixelHeight	Input	number	0.0002	Height in meters of the pixel
PixelSpacing	Input	number	0.008	Distance between the center of adjacent pixels in a uniform grid (default: 0.008 meters)
BankDistanceFromSample	Input	number	5	The distance along the beam direction from the sample to bank in meters (default:5.0)
SourceDistanceFromSample	Input	number	10	The distance along the beam direction from the source to the sample in meters (default:10.0)

Description

Creates sample workspaces for usage examples and other situations.

You can select a predefined function for the data or enter your own by selecting User Defined in the drop down.

The data will be the same for each spectrum, and is defined by the function selected, and a little noise if Random is selected. All values are taken converted to absolute values at present so negative values will become positive. For event workspaces the intensity of the graph will be affected by the number of events selected.

Here is an example of a user defined formula containing two peaks and a background.:

"name=LinearBackground, A0=0.5;
name=Gaussian, PeakCentre=10000, Height=50, Sigma=0.5;
name=Gaussian, PeakCentre=1000, Height=80, Sigma=0.5"

Random also affects the distribution of events within bins for event workspaces. If Random is selected the results will differ between runs of the algorithm and will not be comparable. If comparing the output is important set Random to false or uncheck the box.

Note

For the Quasielastic and Quasielastic Tunnelling presets the XMin and XMax values should be set to a range symmetrical around x=0.

Instrument

The instrument created by CreateSample workspace is very simple and looks like this.

The sample is placed at the origin. The source is separated from the sample in the negative direction by the value you specify in “SourceDistanceFromSample”. The instrument has “NumBanks” detector banks, each bank is moved down the Z axis by “BankDistanceFromSample” from the sample or the previous bank.

Each bank is a square rectangular bank comprising of “BankPixelWidth” pixels in width and height. The size of each pixel 4mm square, but additional padding can be set using “PixelSpacing”.

If “NumMonitors” is also given the first monitor is created half-way between the sample and the first bank, then between each bank (or where the banks would be if “NumMonitors” > “NumBanks”).

If “NumScanPoints” > 1 then a scanning workspace is created, that is one with time indexed positions and rotations. The scan is set up such that for each scan point all the detectors are rotated by 1 degree around the sample.

The following algorithm properties belong to a property group called “Instrument”, and appear in the following order: NumMonitors BankDistanceFromSample SourceDistanceFromSample NumBanks BankPixelWidth PixelWidth PixelSpacing

Usage

Example - create a simple histogram workspace:

# create histogram workspace
ws = CreateSampleWorkspace()

print("Number of spectra: {}".format(ws.getNumberHistograms()))
print("Number of bins: {}".format(ws.blocksize()))
print("Each spectra has a level backgound of {} counts and a peak in the centre of {} counts.".format(ws.readY(0)[0], ws.readY(0)[50]))

Output:

Number of spectra: 200
Number of bins: 100
Each spectra has a level backgound of 0.3 counts and a peak in the centre of 10.3 counts.

Example - create a simple event workspace:

# create event workspace
ws = CreateSampleWorkspace("Event")

print("Number of spectra: {}".format(ws.getNumberHistograms()))
print("Number of bins: {}".format(ws.blocksize()))
print("Number of events: {}".format(ws.getNumberEvents()))
print("Event Workspaces come with bins set by default to a bin width of {}".format(ws.readX(0)[1]-ws.readX(0)[0]))
#The data itensity of an EventWorkspce is scaled by the number of events used, so the values differ from the histogram above.
print("Each spectra has a level backgound of {} counts and a peak in the centre of {} counts.".format(ws.readY(0)[0], ws.readY(0)[50]))

Output:

Number of spectra: 200
Number of bins: 100
Number of events: 190000
Event Workspaces come with bins set by default to a bin width of 200.0
Each spectra has a level backgound of 7.0 counts and a peak in the centre of 257.0 counts.

Example - Using the preset functions:

# create a workspace with Flat Background
wsFlat = CreateSampleWorkspace("Histogram","Flat background")
print("Flat background has a constant value of {} counts.".format(wsFlat.readY(0)[0]))

# create a workspace with multiple peaks
wsMulti = CreateSampleWorkspace("Histogram","Multiple Peaks")
print("Multiple Peaks has a level backgound of {} counts and two gaussian peaks, the largest of which is {} counts.".
      format(wsMulti.readY(0)[0], wsMulti.readY(0)[60]))

# create a workspace with Exponential Decay
wsExp = CreateSampleWorkspace("Histogram","Exp Decay")
print("Exp Decay starts high and drops rapidly to {:.2f} counts at 8,000 us (with the default binning).".format(wsExp.readY(0)[40]))

Output:

Flat background has a constant value of 1.0 counts.
Multiple Peaks has a level backgound of 0.3 counts and two gaussian peaks, the largest of which is 8.3 counts.
Exp Decay starts high and drops rapidly to 0.03 counts at 8,000 us (with the default binning).

Example - Using the your own function:

# create a workspace with data defined using the function string below
myFunc = "name=LinearBackground, A0=0.5;name=Gaussian, PeakCentre=10100, Height=50, Sigma=0.5;name=Gaussian, PeakCentre=1100, Height=80, Sigma=0.5"

ws = CreateSampleWorkspace("Histogram","User Defined",myFunc)

print("My function defined a background of {} counts.".format(ws.readY(0)[0]))
print("With a peak reaching {} counts at 1,100 us,".format(ws.readY(0)[5]))
print("and another reaching {} counts at 10,100 us.".format(ws.readY(0)[50]))

Output:

My function defined a background of 0.5 counts.
With a peak reaching ... counts at 1,100 us,
and another reaching ... counts at 10,100 us.

Example - Quasielastic:

ws=CreateSampleWorkspace(Function="Quasielastic",
                         XUnit="DeltaE",
                         XMin=-0.5,
                         XMax=0.5,
                         BinWidth=0.01)

print("Number of spectra: {}".format(ws.getNumberHistograms()))
print("Number of bins: {}".format(ws.blocksize()))

Output:

Number of spectra: ...
Number of bins: ...

Example - Setting every Option:

#Random adds a little random noise to the data function
ws=CreateSampleWorkspace(WorkspaceType="Event",Function="One Peak",NumBanks=4,NumMonitors=3,BankPixelWidth=5,NumEvents=500,Random=True,XUnit="tof",XMin=0, XMax=8000, BinWidth=100)

print("Number of spectra: {}".format(ws.getNumberHistograms()))
print("Number of bins: {}".format(ws.blocksize()))

Output:

Number of spectra: ...
Number of bins: ...

Categories: AlgorithmIndex | Utility\Workspaces

Source

C++ header: CreateSampleWorkspace.h

C++ source: CreateSampleWorkspace.cpp