.. _method-multilevel_function_train-allocation_control-rank_sampling:

"""""""""""""
rank_sampling
"""""""""""""


Sample allocation based on rank sampling within multilevel function train


.. toctree::
   :hidden:
   :maxdepth: 1



**Specification**

- *Alias:* None

- *Arguments:* None


**Description**


Multilevel function train based on regression may allocate the number
of samples per level based on the collocation ratio times the
regression size.  The regression size is determined by the rank per
core and the basis order per dimension as described at
:dakkw:`model-surrogate-global-function_train`, where these ranks and orders
may be either user-specified values (for initial sample allocation),
incremented values (for external adaptation by Dakota), or recovered
values (in the case of internal C3 adaptation using ``adapt_rank``).

The adaptive algorithm starts from a pilot sample, shapes the profile
based on the regression size computed from the current orders and recovered
ranks, and iterates until convergence.

This capability is \b experimental and under active development.



**Examples**


This example starts with rank-two order-two initial expansion for each
level, with twice as many samples as regression coefficients.  As the
recovered rank is updated for each level, as dictated by the internal
``adapt_rank`` approach, the number of samples is incremented as needed
in order to synchronize with the specified collocation ratio.  In this
case, the basis order is fixed and only the ranks and associated samples
are updated for each level.


.. code-block::

    method,
     model_pointer = 'HIERARCH'
     multifidelity_function_train
       allocation_control rank_sampling
       p_refinement uniform
         start_rank_sequence  = 2 2 2 2 2
         adapt_rank  kick_rank = 2  max_rank  = 10
         start_order_sequence = 2 2 2 2 2
         collocation_ratio = 2.  seed = 160415
         convergence_tolerance = 1.e-2
         max_refinement_iterations = 5




