.. algorithm::

.. summary::

.. relatedalgorithms::

.. properties::

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

This utility algorithm attempts to search for the elastic peak position (EPP) in each spectrum of the given workspace. The algorithm estimates the starting parameters and performs Gaussian fit using the :ref:`algm-Fit` algorithm.

.. note::
    This algorithm uses very simple approach to search for an elastic peak: it suggests that the elastic peak has maximal intensity. This approach may fail in the case if the dataset contains Bragg peaks with higher intensities.

As a result, :ref:`TableWorkspace <Table Workspaces>` with the following columns is produced: *WorkspaceIndex*, *PeakCentre*, *PeakCentreError*, *Sigma*, *SigmaError*, *Height*, *HeightError*, *chiSq* and *FitStatus*. Table rows correspond to the workspace indices.

Last column will contain the status of peak finding as follows:

* **success** : If the fit succeeded, the row is populated with the corresponding values obtained by the fit.
* **fitFailed** : If the fit failed (for whatever reason). A debug message will be logged with a detailed failure message from the fit algorithm. *PeakCentre* is filled with the maximum.
* **narrowPeak** : If there are `<3` bins around the maximum, that have `>0.5*MAX`. An information is logged, fit is not tried. *PeakCentre* is filled with the maximum.
* **negativeMaximum** : If the maximum of the spectrum is not positive. A message will be logged in notice channel. Fit is not attempted.

Usage
-----
**Example: Find EPP in the given workspace.**

.. testcode:: ExFindEPP

    # create sample workspace
    ws = CreateSampleWorkspace(Function="User Defined", UserDefinedFunction="name=LinearBackground, \
                A0=0.3;name=Gaussian, PeakCentre=6000, Height=5, Sigma=75", NumBanks=2, BankPixelWidth=1,
                XMin=4005.75, XMax=7995.75, BinWidth=10.5, BankDistanceFromSample=4.0)

    # search for elastic peak positions
    table = FindEPP(ws)

    # print some results
    print("The fit status is {}".format(table.row(0)['FitStatus']))
    print("The peak centre is at {} microseconds".format(round(table.row(0)['PeakCentre'], 2)))
    print("The peak height is {}".format(round(table.row(0)['Height'],2)))

Output:

.. testoutput:: ExFindEPP

    The fit status is success
    The peak centre is at ... microseconds
    The peak height is ...


.. categories::

.. sourcelink::
   :filename: FindEPP
   :py: None