.. _physics-mergerTreeMassResolution:

Merger Tree Building Mass Resolutions
=====================================

Class providing the minimum progenitor halo mass (mass resolution) to resolve when building a merger tree. Branches below this mass are not followed individually; instead their accreted mass is treated as smooth, unresolved accretion onto the main progenitor. The mass resolution controls the trade-off between completeness of the merger history and computational cost, and can be set as a fixed value, a fraction of the root halo mass, or adaptively based on tree size.

**Default implementation:** ``mergerTreeMassResolutionFixed``

Methods
-------

``resolution`` → ``double precision``
   Gives the mass resolution to use for the given tree.

   * ``type(mergerTree), intent(in ) :: tree``

.. _physics-mergerTreeMassResolutionFixed:

``mergerTreeMassResolutionFixed``
---------------------------------

A merger tree mass resolution class which assumes a fixed, uniform mass resolution applied to all merger trees during tree construction. The minimum resolved halo mass is set by the ``[massResolution]`` parameter, expressed in Solar masses, below which branches are not built.

**(Default implementation)**

**Parameters**

* ``[massResolution]`` (real; default ``5.0d9``) — The mass resolution to use when building merger trees.

.. _physics-mergerTreeMassResolutionScaled:

``mergerTreeMassResolutionScaled``
----------------------------------

A merger tree mass resolution class which computes the mass resolution to be min(``[massResolutionMaximum]``,max(``[massResolutionMinimum]``,\ ``[massResolutionFractional]``\ :math:`\times M_\mathrm{base}`)), where :math:`M_\mathrm{base}` is the base mass of the merger tree.

**Parameters**

* ``[massResolutionMinimum]`` (real; default ``5.0d9``) — The minimum mass resolution to use when building merger trees.
* ``[massResolutionMaximum]`` (real; default ``huge(0.0d0)``) — The maximum mass resolution to use when building merger trees.
* ``[massResolutionFractional]`` (real; default ``1.0d-3``) — The fraction of the tree's root node mass to be used for the mass resolution when building merger trees.