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.. algorithm::
.. summary::
.. alias::
.. properties::
Description
-----------
Reduces a single TOF reflectometry run into a mod Q vs I/I0 workspace.
Performs transmission corrections. Handles both point detector and
multidetector cases. The algorithm can correct detector locations based
on an input theta value.
Historically the work performed by this algorithm was known as the Quick
script.
If :literal:`MonitorBackgroundWavelengthMin` and
:literal:`MonitorBackgroundWavelengthMax` are both set to :literal:`0`, then
background normalization will not be performed on the monitors.
Analysis Modes
The default analysis mode is *PointDetectorAnalysis*. For PointAnalysisMode the
analysis can be roughly reduced to IvsLam = DetectorWS / sum(I0) /
TransmissionWS / sum(I0). For MultiDetectorAnalysis the analysis can be roughly reduced to
IvsLam = DetectorWS / RegionOfDirectBeamWS / sum(I0) / TransmissionWS / sum(I0).
The normalization by tranmission run(s) is optional.
If necessary, input workspaces are converted to *Wavelength*
first via :ref:`algm-ConvertUnits`.
IvsQ is calculated via :ref:`algm-ConvertUnits` into units of
*MomentumTransfer*. Corrections may be applied prior to the
transformation to ensure that the detectors are in the correct location
according to the input Theta value. Corrections are only enabled when a
Theta input value has been provided.
Transmission Runs
Transmission correction is a normalization step, which may be applied to both
*PointDetectorAnalysis* and *MultiDetectorAnalysis* reduction.
Transmission runs are expected to be in TOF. The spectra numbers in the
Transmission run workspaces must be the same as those in the Input Run
workspace. If two Transmission runs are provided then the Stitching
parameters associated with the transmission runs will also be required.
If a single Transmission run is provided, then no stitching parameters
will be needed.
Polynomial Correction
#####################
If no Transmission runs are provided, then polynomial correction can be
performed instead. Polynomial correction is enabled by setting the
:literal:`CorrectionAlgorithm` property. If set to
:literal:`PolynomialCorrection` it runs the :ref:`algm-PolynomialCorrection`
algorithm, with this algorithms :literal:`Polynomial` property used as its
:literal:`Coefficients` property.
If the :literal:`CorrectionAlgorithm` property is set to
:literal:`ExponentialCorrection`, then the :Ref:`algm-ExponentialCorrection`
algorithm is used, with C0 and C1 taken from the :literal:`C0` and :literal:`C1`
properties.
Detector Position Correction
############################
Detector Position Correction is used for when the position of the detector
is not aligned with the reflected beamline. The correction algorithm used is
:ref:`algm-SpecularReflectionPositionCorrect-v1` which is a purely vertical
position correction.
Post-Processing Options
#######################
ReflectometryReductionOne contains 2 post-processing options that will be applied to the IvsQ workspace. These two options are `Scale` and `Rebin`.
Rebinning
=========
To Rebin your IvsQ workspace you will have to provide values for the following properties: `MomentumTransferMinimum`, `MomentumTransferStep` and `MomentumTransferMaximum`.
These values will be appended to each other to form your :ref:`algm-Rebin` Params. These values correspond to your `MinimumExtent`, `BinWidth` and `MaximumExtent` respectively.
If you provide a positive `MomentumTransferStep` value then the algorithm will automatically negate this value which will allow for Logarithmic Rebinning. Alternatively,
a negative `MomentumTransferStep` will result in Linear Rebinning. More details about the Rebinning process can be found in the documentation for :ref:`algm-Rebin`.
If no values are provided for `MomentumTransferMinimum` and `MomentumTransferMaximum` then the algorithm will attempt to calculate these values
by using the equations below:
:math:`Q_{min} = 2 \, k \, sin \, \theta = \frac{4 \pi sin \theta}{\lambda_{max}}`
:math:`Q_{max} = 2 \, k \, sin \, \theta = \frac{4 \pi sin \theta}{\lambda_{min}}`
Where :math:`\lambda_{min}` is the minimum extent of the `IvsLambda` Workspace and :math:`\lambda_{max}` is the maximum extent of the `IvsLambda` Workspace.
If you have not provided a value for `MomentumTransferStep` then the algorithm will use :ref:`algm-CalculateResolution` to calculate this value for you.
Scaling
=======
To apply a scaling to the IvsQ workspace that has been produced by the reduction, you will need to provide a value for the `ScaleFactor` property in the algorithm.
The default for this value is 1.0 and thus no scaling is applied to the workspace. The scaling of the IvsQ workspace is performed in-place by the :ref:`algm-Scale` algorithm
and your IvsQ workspace will be set to the product of this algorithm.
Workflow
########
.. diagram:: ReflectometryReductionOne-v1_wkflw.dot
Source Rotation
###############
In the workflow diagram above, after we produce the IvsLambda workspace, it may be necessary to rotate the position of the source to match the value of ThetaOut (:math:`\theta_f`).
Below we see the typical experimental setup for a Reflectometry instrument. The source direction (Beam vector) is along the horizon. This setup is defined in the Instrument Defintion File
and this instrument setup will be attached to any workspaces associated with that instrument.
When we pass the IvsLambda workspace to :ref:`algm-ConvertUnits` to produce an IvsQ workspace, :ref:`algm-ConvertUnits` will assume that :math:`2\theta` is the angle between the Beam vector and
the sample-to-detector vector. When we have the typical setup seen below, :math:`2\theta` will be exactly half the value we wish it to be.
.. figure:: /images/CurrentExperimentSetupForReflectometry.png
:width: 650px
:height: 250px
:align: center
We rotate the position of the Source (and therefore the Beam vector) in the Instrument Defintion associated with the IvsLambda workspace
until the condition :math:`\theta_i = \theta_f` is satisfied. This will achieve the desired result for :math:`2\theta` (see below for rotated source diagram).
After :ref:`algm-ConvertUnits` has produced our IvsQ workspace, we will rotate the position of the source back to its original position so that the experimental setup remains unchanged for other
algorithms that may need to manipulate/use it.
.. figure:: /images/RotatedExperimentSetupForReflectometry.png
:width: 650px
:height: 250px
:align: center
Usage
-----
**Example - Reduce a Run**
.. testcode:: ExReflRedOneSimple
run = Load(Filename='INTER00013460.nxs')
# Basic reduction with no transmission run
IvsQ, IvsLam, thetaOut = ReflectometryReductionOne(InputWorkspace=run, ThetaIn=0.7, I0MonitorIndex=2, ProcessingInstructions='3:4',
WavelengthMin=1.0, WavelengthMax=17.0,
MonitorBackgroundWavelengthMin=15.0, MonitorBackgroundWavelengthMax=17.0,
MonitorIntegrationWavelengthMin=4.0, MonitorIntegrationWavelengthMax=10.0 )
print "The first four IvsLam Y values are: [ %.4e, %.4e, %.4e, %.4e ]" % (IvsLam.readY(0)[0], IvsLam.readY(0)[1], IvsLam.readY(0)[2], IvsLam.readY(0)[3])
print "The first four IvsQ Y values are: [ %.4e, %.4e, %.4e, %.4e ]" % (IvsQ.readY(0)[0], IvsQ.readY(0)[1], IvsQ.readY(0)[2], IvsQ.readY(0)[3])
print "Theta out is the same as theta in:",thetaOut
Output:
.. testoutput:: ExReflRedOneSimple
The first four IvsLam Y values are: [ 0.0000e+00, 0.0000e+00, 4.9588e-07, 1.2769e-06 ]
The first four IvsQ Y values are: [ 6.2230e-04, 7.7924e-04, 9.1581e-04, 1.0967e-03 ]
Theta out is the same as theta in: 0.7
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.. sourcelink::