.. _automatic_beam_matching:

Automatic Beam Matching
=======================

QuickNXS can automatically match direct beams to loaded runs.
For this to work, the direct beam candidates must already be loaded.
The algorithm selects a best match based on wavelength :math:`\lambda` and the three horizontal slit widths.

Firstly, wavelengths between direct beam and reflectometry run are checked if they match to within a tolerance (default 0.05 nm).
If the wavelengths match, then a parameter distance is computed with the three horizontal slit widths:

.. math::
    d = \sqrt{(a_1 - b_1)^2 + (a_2 - b_2)^2 + (a_3 - b_3)^2}

where :math:`d` is the distance, :math:`a_i` represents the :math:`i` th slit width of the scattered run,
and :math:`b_i` is the :math:`i` th slit width of the direct beam run.

The match is made with the direct beam run with the lowest parameter distance that *also* matches the wavelength within tolerance.

- A: Automatically match direct beams

    .. figure::
        ../images/select_auto_normalization.png
        :alt: Auto select normalization

    Under Tools.
    When this setting is enabled, on load of a data run, it will be automatically checked
    against all loaded direct beam runs to find the best match.


- B: Match Direct Beam button

    .. figure::
        ../images/match_direct_beam_button.png
        :alt: Match Direct Beam button

    Located on the left side underneath the list of possible run numbers.

    In case a match is not automatically found, or a new direct beam is loaded after a run,
    pressing this button will re-match the active (plotted) run with the best direct beam.