Blurb::
Period at which to update derivative-based proposal covariance
Description::
For derivative-based proposal covariance, this specifies the period
(number of accepted MCMC samples) after which the proposal covariance
is updated using derivative values at the current chain point.

*Default Behavior*

When ``update_period`` is not specified, derivatives will inform the
proposal covariance at the start of the chain, but not updated
further.

*Usage Tips*

The ``update_period`` should be tailored to the size of the total chain,
accounting for the relative expense of derivative-based proposal updates.
Topics::

Examples::

.. code-block::

    method,
            bayes_calibration queso
              samples = 2000 seed = 348
              delayed_rejection
              emulator pce sparse_grid_level = 2
              proposal_covariance derivatives
                update_period = 40  # update proposal covariance every 40 points


Theory::

Faq::

See_Also::
