# Changes in version 2.6.1

## Documentation

* `stk_factorialdesign`: Provide missing help text.
  ([ticket #91](https://sourceforge.net/p/kriging/tickets/91/))

* Fix HTML doc (`INDEX` structure was broken).
  

# Changes in version 2.6.0

## Required Octave version

* Required Octave version number has been raised to 3.8.

## Parameter estimation

* `stk_param_init`: The syntax with an additional `do_estim_lnv`
  parameter is now deprecated.  Set model.lognoisevariance to NaN if
  you want an initial estimate for the variance of the noise.

* `stk_param_init_lnv`: Refuse noiseless models (error).

* `stk_model_gpposterior`: Trigger parameter estimation when
  lognoisevariance is NaN.  In the (experimental) case where
  lognoisevariance is a noise model object, parameter estimation is
  triggered as soon as at least one of the optimizable parameters of
  the model is NaN.
  ([ticket #93](https://sourceforge.net/p/kriging/tickets/93/))

* `stk_param_relik`: Return [] instead of NaN when the derivative with
  respect to lnv is requested for a noiseless model.

* `stk_param_relik`: Detect duplicated observation points automatically
  and raise an error for noiseless models.

* `stk_param_getdefaultbounds`: Estimation bounds for the regularity
  parameter of the Matérn covariance function are now customizable through
  the options `nu_min_dimfun` and `nu_max_dimfun`.

## Covariance functions

* Deprecated: `stk_noisecov`.

## Models

* `stk_get_input_data`, `stk_get_output_data`, `stk_get_prior_model`:
  New getters for model properties, that replace `get_input_data`,
  `get_output_data` and `get_prior_model` respectively (now deprecated).

* `stk_get_observation_variances`: New getter, which returns the
  vector of variances associated to the observations that have been
  used to build a model.

* `stk_gaussiannoise_`, `stk_gaussiannoise_het0`: New classes
  representing Gaussian noise models.  Currently in experimental
  state, these two classes are merely a proof-of-concept.  Other noise
  model classes can be defined by subclassing `stk_gaussiannoise_`.
  ([ticket #38](https://sourceforge.net/p/kriging/tickets/38/))

* `stk_example_misc05`: Demonstrate the use of noise model objects
  to estimate the dispersion parameter in an heteroscedatic case.

* `stk_simulate_noise`: New function to simulate noise sample replicates.

## `stk_dataframe` and related classes

* `stk_dataframe`: Accept char vectors (or strings) as `colnames` or
  `rownames` argument when there is only one column or one row
  ([ticket #92](https://sourceforge.net/p/kriging/tickets/92/))

* `@stk_dataframe/sort`: Argument `dim` can now be skipped, as in the
  base `sort` function.

* `@stk_dataframe/unique`: Overload base function.

## Graphics

* `stk_plot1d`: Do not create a legend systematically.
  ([ticket #82](https://sourceforge.net/p/kriging/tickets/82/))

* `stk_legend`: New function to create a legend, using the graphical
  objects for which a non-empty DisplayName has been provided.

* `stk_plot_shadedci`: Change gray levels and improve legend.

## Miscellaneous

* `stk_options_set`: Make it possible to set all options at once using
  an option structure.  Add help text.

* `stk_runtests`: Return test results in a structure.

* `stk_sampling_nesteddesign`: Fix help text.

-----


# Changes in version 2.5.1

## Bug fixes

* `stk_dominatedhv`: Workaround for Octave 4.4 issue
  ([ticket #89](https://sourceforge.net/p/kriging/tickets/89/))

## Miscellaneous

* Documentation fixes.

* `stk_option_set`: Return option struct only if `nargout > 0`.


# Changes in version 2.5.0

## Required Octave version

* Required Octave version number has been raised to 3.6.0.

## Sequential design of experiments

* `stk_sampcrit_akg_eval`: New function.  Computes the Approximate
  Knowledge Gradient (AKG) sampling criterion.

* `stk_example_doe05`: Example script that demonstrates the use of the AKG
  and EQI sampling criteria for noisy optimization.

* New (experimental) classes to represent sampling criterion objects:
  `stk_sampcrit_ei`, `stk_sampcrit_akg`, `stk_sampcrit_eqi`.

* `stk_sampcrit_ei_eval`: Remove deprecated calling forms.

## Design of experiments

* `stk_factorialdesign`: Accept one-variable `stk_dataframe` objects as
  factors and preserve column names in this case.

* `stk_sampling_nesteddesign`: New function to create nested designs.

* `stk_sampling_nestedlhs`: New function to create nested LHS (NLHS).

* `stk_sampling_sobol`: Fix help text.

## Validation of models

* `stk_distrib_normal_crps`: New function to compare observations and
  predictive (Gaussian) density.

* Calling `stk_predict_leaveoneout` with no output arguments now
  automatically creates two cross-validation diagnostics in two subplots:
  prediction VS observations (left panel) and normalized residuals (right
  panel).

* `stk_predict_leaveoneout` uses now the virtual LOO formula.

## `stk_dataframe` and related classes

* `stk_hrect`: Preserve column names for `stk_dataframe` inputs.

* `@stk_dataframe/find`: Overload base function to support calling find
  with an stk_dataframe as first input argument.

* `@stk_dataframe/plotmatrix`: Overload base function to enrich
  `plotmatrix` graphics with variable names when possible.

* Logical functions

   + Operations that normally return logical (`lt`, `eq`, `and`...) now
     return logical values for `stk_dataframe` arguments.

   + New overloaded functions for `stk_dataframe` objects: `isinf`,
     `isnan`, `isfinite`.

* Testing array membership

   + `@stk_dataframe/ismember`: No longer assumes `rows` flag for
     consistency 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