.. algorithm::

.. summary::

.. relatedalgorithms::

.. properties::

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

.. warning::

   This algorithm is being developed for a specific instrument. It might get changed or even
   removed without a notification, should instrument scientists decide to do so.

This algorithm merges given matrix workspaces to a :ref:`Workspace2D <Workspace2D>`. The purpose of this algorithm is to merge the DNS diffraction mode data measured at different detector bank positions. The algorithm is not suitable to merge DNS single crystal diffraction data measured at different sample rotation angles.

.. note::
    The **OutputWorkspace** will have no connection to the instrument. Part of the sample logs will be lost either. This algorithm can be executed at any step of the data reduction to view the result. However, further data reduction must be performed on the original workspaces.

As a result, a workspace containing a single spectrum will be produced. Values on X-axis depend on user's choice.

Absolute value of the momentum transfer :math:`|Q|` is calculated as

:math:`|Q| = \left|\frac{4\pi\sin\theta}{\lambda}\right|`

where :math:`\theta` is the scattering angle and :math:`\lambda` is the neutron wavelength.

d-Spacing :math:`d` is calculated as:

:math:`d = \left|\frac{\lambda}{2\,\sin\theta}\right|`

Valid input workspaces
######################

The input workspaces (**WorkspaceNames**) have to have the following in order to be valid inputs for this algorithm.

-  The same number of dimensions
-  The same number of spectra
-  The same number of bins
-  The same wavelength in the sample logs
-  The same value of *normalized* sample log. Algorithm cannot merge data with different normalizations.

For the physically meaningful merge result, it is also important that these workspaces have the same slits size, polarisation, and flipper status. If some of these parameters are different, algorithm produces warning. If these properties are not specified in the workspace sample logs, no comparison is performed.

Usage
-----

**Example - Merge a set of selected runs**

.. code-block:: python

    from os import listdir
    from os.path import isfile, join, splitext
    import re
    import numpy as np

    # path to the directory containing data files
    mypath = "/path/to/data/dns/rc36b_standard_dz"
    coilcurrents = join(mypath, 'currents.txt')

    # filter the data files in the given directory
    p = re.compile(r'^dz(\d{8})vana.d_dat$')

    # we choose only the runs with 'x' polarisation
    filelist = [str(i*6 + 29100501) for i in range(10)]

    def is_in_filelist(fname, p, flist):
        m = re.match(p, fname)
        if m:
            num = m.group(1)
            return num in flist
        else:
            return False

    datafiles = sorted([f for f in listdir(mypath) if isfile(join(mypath,f)) and is_in_filelist(f, p, filelist)])

    # load data to workspaces
    wslist = []
    for f in datafiles:
        try:
            wname = splitext(f)[0]
            #print("Processing {}".format(wname))  # uncomment if needed
            LoadDNSLegacy(Filename=join(mypath, f), OutputWorkspace=wname, CoilCurrentsTable=coilcurrents, Normalization='duration')
        except RuntimeError as err:
            print(err)
        else:
            wslist.append(wname)

    # merge the given workspaces
    merged = DNSMergeRuns(wslist, HorizontalAxis='2theta')
    mergedQ = DNSMergeRuns(wslist, HorizontalAxis='|Q|')
    mergedD = DNSMergeRuns(wslist, HorizontalAxis='d-Spacing')

    # print selected values from merged workspaces
    two_theta = merged.extractX()[0]
    print("First 5 2Theta values: {}".format(two_theta[:5]))
    q = mergedQ.extractX()[0]
    print("First 5 |Q| values: {}".format(np.round(q[:5], 3)))
    d = mergedD.extractX()[0]
    print("First 5 d values: {}".format(np.round(d[:5], 3)))

Output:

   First 5 2Theta values: [ 7.5  8.   8.5  9.   9.5]

   First 5 Q values: [ 0.249  0.266  0.282  0.299  0.315]

   First 5 d values: [ 1.844  1.848  1.852  1.856  1.86 ]

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