.. _model-surrogate-non_hierarchical-unordered_model_fidelities:

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unordered_model_fidelities
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Specification of an unordered ensemble of low-fidelity approximations


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



**Specification**

- *Alias:* approximation_models 

- *Arguments:* STRINGLIST


**Description**


A ``non_hierarchical`` surrogate model manages an unordered set of
low-fidelity model approximations, each of which may include hyper-parameter
resolution controls (in the case of a simulation model) or additional model
recursions.

Any corresponding sequence specifications within methods (e.g.,
``quadrature_order_sequence``, ``sparse_grid_level_sequence``,
``expansion_order_sequence``, etc. within stochastic expansion methods)
should be synchronized with the order in the model listing.

Internal to the non-hierarchical model, subsets of the model ensemble
may be active for any given evaluation, as dictated by the iterative
algorithm in use.



**Examples**



.. code-block::

    model,
     id_model = 'NONHIERARCH'
     surrogate non_hierarchical
       unordered_model_fidelities = 'LF1' 'LF2'
       truth_model_pointer = 'HF'
    
    model,
     id_model = 'LF1'
     simulation
       interface_pointer = 'LF1_DRIVER'
              solution_level_cost = 1.
    
    model,
     id_model = 'LF2'
     simulation
       interface_pointer = 'LF2_DRIVER'
              solution_level_cost = 2.4
    
    model,
     id_model = 'HF'
     simulation
       interface_pointer = 'HF_DRIVER'
              solution_level_cost = 256.