.. _method-multilevel_sampling-solution_mode-offline_projection:

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offline_projection
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Specify a solution mode that estimates performance based on projecting
initial correlation/variance estimates from an offline pilot sample



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**Specification**

- *Alias:* None

- *Arguments:* None


**Description**


Multilevel / multifidelity sampling methods are adaptive UQ methods
that utilize a pilot sample to estimate an initial set of correlations
or covariances, which is then used to initiate the process of
performance estimation and resource allocation.  In online and offline
projection modes, evaluations are limited to the pilot sample and
these initial correlation / covariance estimates are used to project
the potential estimator performance, without any further sampling and
without any computation of statistics.  For the offline projection case,
the estimator performance is computed with an online sample allocation
that is unconstrained by the offline pilot.

**Usage Tips**

This mode is useful for comparing the projected performance of different
estimators, which can inform method selection.

Note that the sample allocation for each model is lower bounded at two
samples for defining nonzero variance.  While not required for projecting
estimator performance, this enables consistency with the corresponding
non-projection mode that may follow.