.. _method-multilevel_sampling-solution_mode-online_projection:

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online_projection
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Specify a solution mode that estimates performance based on projecting
initial correlation / covariance estimates from an online 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 online projection case,
the estimator performance is computed with an online pilot sample as
a lower bound on the total sampling allocation.

**Usage Tips**

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