.. algorithm::

.. summary::

.. relatedalgorithms::

.. properties::

Description
-----------

Converts a 2D workspace from :ref:`units <Unit Factory>`
of spectrum number/**energy transfer**
to the intensity as a function of **momentum transfer** :math:`Q`
and **energy transfer** :math:`\Delta E`.

The details of the Normalised Polygon technique for rebinning are given in
:ref:`FractionalRebinning <FractionalRebinning>`.

The algorithm operates in *non-PSD mode* by default. This means that the
scattering angle :math:`2\theta` range covered by a detector is calculated for
each detector individually. For grouped detectors, it is the minimum and
maximum :math:`2\theta` of all detectors in the group. The computation is
accurate for simple detector shapes (cylinder, cuboid); for other shapes a
more rough method is used. It is possible to provide precalculated
per-detector :math:`2\theta` values using the ``DetectorTwoThetaRanges`` input
property.

*PSD mode* will determine the detector :math:`2\theta` ranges from the
instrument geometry. This mode is activated by placing the following named
parameter in the instrument definition file: *detector-neighbour-offset*. The
integer value of this parameter should be the number of pixels that separates
two pixels at the same vertical position in adjacent tubes.

See :ref:`algm-SofQWCentre` for centre-point binning or :ref:`algm-SofQWPolygon`
for simpler and less precise but faster binning strategies. The speed-up
is from ignoring the azimuthal positions of the detectors (as for the non-PSD
mode in this algorithm) but in addition, :ref:`algm-SofQWPolygon` treats
all detectors as being the same, and characterised by a single width in
scattering angle. Thereafter, it weights the signal and error by the fractional
overlap, similarly to that shown in the first figure above, but then discards
the summed weights, producing a **Workspace2D** rather than a
**RebinnedOutput** workspace.

Usage
-----

**Example - simple transformation of inelastic workspace:**

.. testcode:: SofQWNormalisedPolygon

   # create sample inelastic workspace for MARI instrument containing 1 at all spectra
   ws=CreateSimulationWorkspace(Instrument='MAR',BinParams='-10,1,10')
   # convert workspace into Matrix workspace with Q-dE coordinates
   ws=SofQWNormalisedPolygon(InputWorkspace=ws,QAxisBinning='-3,0.1,3',Emode='Direct',EFixed=12)

   print("The converted X-Y values are:")
   Xrow=ws.readX(59);
   Yrow=ws.readY(59);
   line1= " ".join('! {0:>6.2f} {1:>6.2f} '.format(Xrow[i],Yrow[i]) for i in range(0,10))
   print(line1 + " !")
   line2= " ".join('! {0:>6.2f} {1:>6.2f} '.format(Xrow[i],Yrow[i]) for i in range(10,20))
   print(line2 + " !")
   print('! {0:>6.2f} ------- !'.format(Xrow[20]))



.. testcleanup:: SofQWNormalisedPolygon

   DeleteWorkspace(ws)

**Output:**

.. testoutput:: SofQWNormalisedPolygon

   The converted X-Y values are:
   ! -10.00   1.00  !  -9.00   1.00  !  -8.00   1.00  !  -7.00   1.00  !  -6.00   1.00  !  -5.00   1.00  !  -4.00   1.00  !  -3.00   1.00  !  -2.00   1.00  !  -1.00   1.00  !
   !   0.00   1.00  !   1.00   1.00  !   2.00   1.00  !   3.00   1.00  !   4.00   1.00  !   5.00   1.00  !   6.00   1.00  !   7.00   1.00  !   8.00   1.00  !   9.00   1.00  !
   !  10.00 ------- !


.. categories::

.. sourcelink::